From 417d5b80bfb58654c13b70c08d83d2a22add3a61 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Sat, 28 Aug 2021 22:56:15 +0800
Subject: [PATCH 01/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200134.=E5=8A=A0?=
 =?UTF-8?q?=E6=B2=B9=E7=AB=99.md=20C=E8=AF=AD=E8=A8=80=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0134.加油站.md | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/problems/0134.加油站.md b/problems/0134.加油站.md
index 0befd085..ff54fbc6 100644
--- a/problems/0134.加油站.md
+++ b/problems/0134.加油站.md
@@ -283,6 +283,30 @@ var canCompleteCircuit = function(gas, cost) {
 };
 ```
 
+C:
+```c
+int canCompleteCircuit(int* gas, int gasSize, int* cost, int costSize){
+    int curSum = 0;
+    int i;
+    int min = INT_MAX;
+    for(i = 0; i < gasSize; i++) {
+        int diff = gas[i] - cost[i];
+        curSum += diff;
+        if(min > curSum)
+            min = curSum;
+    }
+    if(curSum < 0)
+        return -1;
+    if(min >= 0)
+        return 0;
+    for(i = gasSize - 1; i >= 0; i--) {
+        min+=(gas[i]-cost[i]);
+        if(min >= 0)
+            return i;
+    }
+    return 0;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 6333521adf7e6204a55dbb2c1f831429f688c4ea Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Sun, 29 Aug 2021 10:28:15 +0800
Subject: [PATCH 02/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200452.=E7=94=A8?=
 =?UTF-8?q?=E6=9C=80=E5=B0=91=E6=95=B0=E9=87=8F=E7=9A=84=E7=AE=AD=E5=BC=95?=
 =?UTF-8?q?=E7=88=86=E6=B0=94=E7=90=83.md=20C=E8=AF=AD=E8=A8=80=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../0452.用最少数量的箭引爆气球.md | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/problems/0452.用最少数量的箭引爆气球.md b/problems/0452.用最少数量的箭引爆气球.md
index 7b8130f0..a2168dfc 100644
--- a/problems/0452.用最少数量的箭引爆气球.md
+++ b/problems/0452.用最少数量的箭引爆气球.md
@@ -218,6 +218,30 @@ var findMinArrowShots = function(points) {
 };
 ```
 
+C:
+```c
+int cmp(const void *a,const void *b)
+{
+    return ((*((int**)a))[0] > (*((int**)b))[0]);
+} 
+
+int findMinArrowShots(int** points, int pointsSize, int* pointsColSize){
+    //将points数组作升序排序
+    qsort(points, pointsSize, sizeof(points[0]),cmp);
+    
+    int arrowNum = 1;
+    int i = 1;
+    for(i = 1; i < pointsSize; i++) {
+        //若前一个气球与当前气球不重叠，证明需要增加箭的数量
+        if(points[i][0] > points[i-1][1])
+            arrowNum++;
+        else
+            //若前一个气球与当前气球重叠，判断并最小的x_end
+            points[i][1] = points[i][1] > points[i-1][1] ? points[i-1][1] : points[i][1];
+    }
+    return arrowNum;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From d327806115b66777e8e19ee27af10d4491b7a609 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Sun, 29 Aug 2021 10:37:39 +0800
Subject: [PATCH 03/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200134.=E5=8A=A0?=
 =?UTF-8?q?=E6=B2=B9=E7=AB=99.md=20C=E8=AF=AD=E8=A8=80=E7=89=88=E6=9C=AC?=
 =?UTF-8?q?=E6=B3=A8=E9=87=8A?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0134.加油站.md | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/problems/0134.加油站.md b/problems/0134.加油站.md
index ff54fbc6..ff3bc8b2 100644
--- a/problems/0134.加油站.md
+++ b/problems/0134.加油站.md
@@ -289,21 +289,26 @@ int canCompleteCircuit(int* gas, int gasSize, int* cost, int costSize){
     int curSum = 0;
     int i;
     int min = INT_MAX;
+    //遍历整个数组。计算出每站的用油差。并将其与最小累加量比较
     for(i = 0; i < gasSize; i++) {
         int diff = gas[i] - cost[i];
         curSum += diff;
-        if(min > curSum)
+        if(curSum < min)
             min = curSum;
     }
+    //若汽油总数为负数，代表无法跑完一环。返回-1
     if(curSum < 0)
         return -1;
+    //若min大于等于0，说明每一天加油量比用油量多。因此从0出发即可
     if(min >= 0)
         return 0;
+    //若累加最小值为负，则找到一个非零元素（加油量大于出油量）出发。返回坐标
     for(i = gasSize - 1; i >= 0; i--) {
         min+=(gas[i]-cost[i]);
         if(min >= 0)
             return i;
     }
+    //逻辑上不会返回这个0
     return 0;
 }
 ```

From cbdc4bd369541f15f504d71c4203a452a7e9ca65 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Sun, 29 Aug 2021 10:40:41 +0800
Subject: [PATCH 04/57] =?UTF-8?q?=E6=9B=B4=E6=96=B0=200452.=E7=94=A8?=
 =?UTF-8?q?=E6=9C=80=E5=B0=91=E6=95=B0=E9=87=8F=E7=9A=84=E7=AE=AD=E5=BC=95?=
 =?UTF-8?q?=E7=88=86=E6=B0=94=E7=90=83.md=20C=E8=AF=AD=E8=A8=80=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC=E6=B3=A8=E9=87=8A?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0452.用最少数量的箭引爆气球.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/problems/0452.用最少数量的箭引爆气球.md b/problems/0452.用最少数量的箭引爆气球.md
index a2168dfc..07141558 100644
--- a/problems/0452.用最少数量的箭引爆气球.md
+++ b/problems/0452.用最少数量的箭引爆气球.md
@@ -236,7 +236,7 @@ int findMinArrowShots(int** points, int pointsSize, int* pointsColSize){
         if(points[i][0] > points[i-1][1])
             arrowNum++;
         else
-            //若前一个气球与当前气球重叠，判断并最小的x_end
+            //若前一个气球与当前气球重叠，判断并更新最小的x_end
             points[i][1] = points[i][1] > points[i-1][1] ? points[i-1][1] : points[i][1];
     }
     return arrowNum;

From b4858a21cdf7a154e84fd3825b031740a7a6db08 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Sun, 29 Aug 2021 10:58:53 +0800
Subject: [PATCH 05/57] =?UTF-8?q?=E4=BF=AE=E5=A4=8D1005.K=E5=8F=96?=
 =?UTF-8?q?=E5=8F=8D=E5=90=8E=E6=9C=80=E5=A4=A7=E5=8C=96=E7=9A=84=E6=95=B0?=
 =?UTF-8?q?=E7=BB=84=E5=92=8CJava=E4=BB=A3=E7=A0=81K=E4=B9=A6=E5=86=99?=
 =?UTF-8?q?=E9=94=99=E8=AF=AF=E9=97=AE=E9=A2=98?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/1005.K次取反后最大化的数组和.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/problems/1005.K次取反后最大化的数组和.md b/problems/1005.K次取反后最大化的数组和.md
index 8bdd0f41..b9973b5f 100644
--- a/problems/1005.K次取反后最大化的数组和.md
+++ b/problems/1005.K次取反后最大化的数组和.md
@@ -110,13 +110,13 @@ class Solution {
 	int len = nums.length;	    
 	for (int i = 0; i < len; i++) {
 	    //从前向后遍历，遇到负数将其变为正数，同时K--
-	    if (nums[i] < 0 && k > 0) {
+	    if (nums[i] < 0 && K > 0) {
 	    	nums[i] = -nums[i];
-		k--;
+            K--;
 	    }
 	}
 	// 如果K还大于0，那么反复转变数值最小的元素，将K用完
-	if (k % 2 == 1) nums[len - 1] = -nums[len - 1];
+	if (K % 2 == 1) nums[len - 1] = -nums[len - 1];
 	int result = 0;
 	for (int a : nums) {
 	    result += a;

From 051c2c5c3e6e77c757ffb94ba2e8f24f21243cc2 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Sun, 29 Aug 2021 11:02:52 +0800
Subject: [PATCH 06/57] =?UTF-8?q?=E4=BF=AE=E5=A4=8D1005.K=E5=8F=96?=
 =?UTF-8?q?=E5=8F=8D=E5=90=8E=E6=9C=80=E5=A4=A7=E5=8C=96=E7=9A=84=E6=95=B0?=
 =?UTF-8?q?=E7=BB=84=E5=92=8CJava=E4=BB=A3=E7=A0=81K=E4=B9=A6=E5=86=99?=
 =?UTF-8?q?=E9=94=99=E8=AF=AF=E9=97=AE=E9=A2=98?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/1005.K次取反后最大化的数组和.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/problems/1005.K次取反后最大化的数组和.md b/problems/1005.K次取反后最大化的数组和.md
index b9973b5f..0a0c8d62 100644
--- a/problems/1005.K次取反后最大化的数组和.md
+++ b/problems/1005.K次取反后最大化的数组和.md
@@ -112,7 +112,7 @@ class Solution {
 	    //从前向后遍历，遇到负数将其变为正数，同时K--
 	    if (nums[i] < 0 && K > 0) {
 	    	nums[i] = -nums[i];
-            K--;
+	    	K--;
 	    }
 	}
 	// 如果K还大于0，那么反复转变数值最小的元素，将K用完

From 615139b74d11f47116b8b1e08e04936ba6184d72 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Sun, 29 Aug 2021 18:55:36 +0800
Subject: [PATCH 07/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00046.=E5=85=A8=E6=8E=92?=
 =?UTF-8?q?=E5=88=97=E6=96=B0=E8=A7=A3=E6=B3=95Java=E4=BB=A3=E7=A0=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0046.全排列.md | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/problems/0046.全排列.md b/problems/0046.全排列.md
index df9394eb..001c249e 100644
--- a/problems/0046.全排列.md
+++ b/problems/0046.全排列.md
@@ -183,6 +183,32 @@ class Solution {
     }
 }
 ```
+```java
+// 解法2：通过判断path中是否存在数字，排除已经选择的数字
+class Solution {
+    List<List<Integer>> result = new ArrayList<>();
+    LinkedList<Integer> path = new LinkedList<>();
+    public List<List<Integer>> permute(int[] nums) {
+        if (nums.length == 0) return result;
+        backtrack(nums, path);
+        return result;
+    }
+    public void backtrack(int[] nums, LinkedList<Integer> path) {
+        if (path.size() == nums.length) {
+            result.add(new ArrayList<>(path));
+        }
+        for (int i =0; i < nums.length; i++) {
+            // 如果path中已有，则跳过
+            if (path.contains(nums[i])) {
+                continue;
+            } 
+            path.add(nums[i]);
+            backtrack(nums, path);
+            path.removeLast();
+        }
+    }
+}
+```
 
 Python：
 ```python3

From 976379c7f28de998cd2a475c4d693978b55ea03a Mon Sep 17 00:00:00 2001
From: bourne-3 <595962708@qq.com>
Date: Sun, 29 Aug 2021 20:43:26 +0800
Subject: [PATCH 08/57] =?UTF-8?q?0234-=E5=9B=9E=E6=96=87=E9=93=BE=E8=A1=A8?=
 =?UTF-8?q?Java=E5=AE=9E=E7=8E=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0234.回文链表.md | 71 +++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/problems/0234.回文链表.md b/problems/0234.回文链表.md
index 04015a7f..631d2f6b 100644
--- a/problems/0234.回文链表.md
+++ b/problems/0234.回文链表.md
@@ -144,6 +144,75 @@ public:
 ## Java
 
 ```java
+// 方法一，使用数组
+class Solution {
+    public boolean isPalindrome(ListNode head) {
+        int len = 0;
+        // 统计链表长度
+        ListNode cur = head;
+        while (cur != null) {
+            len++;
+            cur = cur.next;
+        }
+        cur = head;
+        int[] res = new int[len];
+        // 将元素加到数组之中
+        for (int i = 0; i < res.length; i++){
+            res[i] = cur.val;
+            cur = cur.next;
+        }
+        // 比较回文
+        for (int i = 0, j = len - 1; i < j; i++, j--){
+            if (res[i] != res[j]){
+                return false;
+            }
+        }
+        return true;
+    }
+}
+
+// 方法二，快慢指针
+class Solution {
+    public boolean isPalindrome(ListNode head) {
+        // 如果为空或者仅有一个节点，返回true
+        if (head == null && head.next == null) return true;
+        ListNode slow = head;
+        ListNode fast = head;
+        ListNode pre = head;
+        while (fast != null && fast.next != null){
+            pre = slow;  // 记录slow的前一个结点
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        pre.next = null;  // 分割两个链表
+
+        // 前半部分
+        ListNode cur1 = head;
+        // 后半部分。这里使用了反转链表
+        ListNode cur2 = reverseList(slow);
+
+        while (cur1 != null){
+            if (cur1.val != cur2.val) return false;
+
+            // 注意要移动两个结点
+            cur1 = cur1.next;
+            cur2 = cur2.next;
+        }
+        return true;
+    }
+    ListNode reverseList(ListNode head){
+        // 反转链表
+        ListNode tmp = null;
+        ListNode pre = null;
+        while (head != null){
+            tmp = head.next;
+            head.next = pre;
+            pre = head;
+            head = tmp;
+        }
+        return pre;
+    }
+}
 ```
 
 ## Python
@@ -209,11 +278,13 @@ class Solution:
 ## Go
 
 ```go
+
 ```
 
 ## JavaScript
 
 ```js
+
 ```
 
 

From 4e2fbce1b2314cf90f2d9f0f149b85a381349e30 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=BD=99=E6=9D=9C=E6=9E=97?=
 <du@yudulindeMacBook-Pro.local>
Date: Sun, 29 Aug 2021 23:15:42 +0800
Subject: [PATCH 09/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00151.=E7=BF=BB=E8=BD=AC?=
 =?UTF-8?q?=E5=AD=97=E7=AC=A6=E4=B8=B2=E9=87=8C=E7=9A=84=E5=8D=95=E8=AF=8D?=
 =?UTF-8?q?=20Swift=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0151.翻转字符串里的单词.md | 79 ++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/problems/0151.翻转字符串里的单词.md b/problems/0151.翻转字符串里的单词.md
index 84e348a9..c4a9c7e0 100644
--- a/problems/0151.翻转字符串里的单词.md
+++ b/problems/0151.翻转字符串里的单词.md
@@ -467,6 +467,85 @@ function reverse(strArr, start, end) {
 }
 ```
 
+Swift:
+
+```swift
+func reverseWords(_ s: String) -> String {
+    var stringArr = removeSpace(s)
+    reverseString(&stringArr, startIndex: 0, endIndex: stringArr.count - 1)
+    reverseWord(&stringArr)
+    return String(stringArr)
+}
+
+/// 1、移除多余的空格（前后所有的空格，中间只留一个空格）
+func removeSpace(_ s: String) -> [Character] {
+    let ch = Array(s)
+    var left = 0
+    var right = ch.count - 1
+    // 忽略字符串前面的所有空格
+    while ch[left] == " " {
+        left += 1
+    }
+    // 忽略字符串后面的所有空格
+    while ch[right] == " " {
+        right -= 1
+    }
+
+    // 接下来就是要处理中间的多余空格
+    var lastArr = Array<Character>()
+    while left <= right {
+        // 准备加到新字符串当中的字符
+        let char = ch[left]
+        // 新的字符串的最后一个字符；或者原字符串中，准备加到新字符串的那个字符；这两个字符当中，只要有一个不是空格，就可以加到新的字符串当中
+        if char != " " || lastArr[lastArr.count - 1] != " "  {
+            lastArr.append(char)
+        }
+      
+        left += 1
+    }
+    return lastArr
+}
+
+/// 2、反转整个字符串
+func reverseString(_ s: inout [Character], startIndex: Int, endIndex: Int)  {
+    var start = startIndex
+    var end = endIndex
+    while start < end {
+        (s[start], s[end]) = (s[end], s[start])
+        start += 1
+        end -= 1
+    }
+}
+
+/// 3、再次将字符串里面的单词反转
+func reverseWord(_ s: inout [Character]) {
+    var start = 0
+    var end = 0
+    var entry = false
+
+    for i in 0..<s.count {
+        if !entry {
+            start = i
+            entry = true
+        }
+      
+        if entry && s[i] == " " && s[i - 1] != " " {
+            end = i - 1
+            entry = false
+            reverseString(&s, startIndex: start, endIndex: end)
+        }
+
+        if entry && (i == s.count - 1) && s[i] != " " {
+            end = i
+            entry = false
+            reverseString(&s, startIndex: start, endIndex: end)
+        }
+    }
+}
+```
+
+
+
 
 
 

From eb17c57bf3c0c3c5785568614073800866770f3f Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Mon, 30 Aug 2021 10:23:08 +0800
Subject: [PATCH 10/57] =?UTF-8?q?=E5=A2=9E=E5=8A=A00134.=E5=8A=A0=E6=B2=B9?=
 =?UTF-8?q?=E7=AB=99Java=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0134.加油站.md | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/problems/0134.加油站.md b/problems/0134.加油站.md
index 0befd085..bee909c3 100644
--- a/problems/0134.加油站.md
+++ b/problems/0134.加油站.md
@@ -200,6 +200,7 @@ public:
 
 Java：
 ```java
+// 解法1
 class Solution {
     public int canCompleteCircuit(int[] gas, int[] cost) {
         int sum = 0;
@@ -221,7 +222,26 @@ class Solution {
     }
 }
 ```
-
+```java
+// 解法2
+class Solution {
+    public int canCompleteCircuit(int[] gas, int[] cost) {
+        int curSum = 0;
+        int totalSum = 0;
+        int index = 0;
+        for (int i = 0; i < gas.length; i++) {
+            curSum += gas[i] - cost[i];
+            totalSum += gas[i] - cost[i];
+            if (curSum < 0) {
+                index = (i + 1) % gas.length ; 
+                curSum = 0;
+            }
+        }
+        if (totalSum < 0) return -1;
+        return index;
+    }
+}
+```
 Python：
 ```python
 class Solution:

From bf068cc17b02bf62bbd2055f49effa5093bd2b4d Mon Sep 17 00:00:00 2001
From: wjjiang <48505670+Spongecaptain@users.noreply.github.com>
Date: Mon, 30 Aug 2021 11:14:24 +0800
Subject: [PATCH 11/57] =?UTF-8?q?Update=200392.=E5=88=A4=E6=96=AD=E5=AD=90?=
 =?UTF-8?q?=E5=BA=8F=E5=88=97.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

添加 Golang 动态规划版本
---
 problems/0392.判断子序列.md | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/problems/0392.判断子序列.md b/problems/0392.判断子序列.md
index 54c16489..784e3bbc 100644
--- a/problems/0392.判断子序列.md
+++ b/problems/0392.判断子序列.md
@@ -203,6 +203,25 @@ const isSubsequence = (s, t) => {
 };
 ```
 
+Go：
+```go
+func isSubsequence(s string, t string) bool {
+    dp := make([][]int,len(s)+1)
+    for i:=0;i<len(dp);i++{
+        dp[i] = make([]int,len(t)+1)
+    }
+    for i:=1;i<len(dp);i++{
+        for j:=1;j<len(dp[i]);j++{
+            if s[i-1] == t[j-1]{
+                dp[i][j] = dp[i-1][j-1] +1
+            }else{
+                dp[i][j] = dp[i][j-1]
+            }
+        }
+    }
+    return dp[len(s)][len(t)]==len(s)
+}
+```
 
 
 

From 969c5c50ea5e73468cacc71bda0ef2894dda8c9b Mon Sep 17 00:00:00 2001
From: YDLIN <1924723909@qq.com>
Date: Mon, 30 Aug 2021 13:17:34 +0800
Subject: [PATCH 12/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=E5=89=91=E6=8C=87Offer?=
 =?UTF-8?q?58-II.=E5=B7=A6=E6=97=8B=E8=BD=AC=E5=AD=97=E7=AC=A6=E4=B8=B2=20?=
 =?UTF-8?q?Swift=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../剑指Offer58-II.左旋转字符串.md    | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/problems/剑指Offer58-II.左旋转字符串.md b/problems/剑指Offer58-II.左旋转字符串.md
index f4d3368c..d8aaca67 100644
--- a/problems/剑指Offer58-II.左旋转字符串.md
+++ b/problems/剑指Offer58-II.左旋转字符串.md
@@ -214,6 +214,34 @@ var reverseLeftWords = function (s, n) {
 };
 ```
 
+Swift:
+
+```swift
+func reverseLeftWords(_ s: String, _ n: Int) -> String {
+    var ch = Array(s)
+    let len = ch.count
+    // 反转区间[0, n - 1]
+    reverseString(&ch, startIndex: 0, endIndex: n - 1)
+    // 反转区间[n, len - 1]
+    reverseString(&ch, startIndex: n, endIndex: len - 1)
+    // 反转区间[0, len - 1]，也就是整个字符串反转
+    reverseString(&ch, startIndex: 0, endIndex: len - 1)
+    return String(ch)
+}
+
+func reverseString(_ s: inout [Character], startIndex: Int, endIndex: Int)  {
+    var start = startIndex
+    var end = endIndex
+    while start < end {
+        (s[start], s[end]) = (s[end], s[start])
+        start += 1
+        end -= 1
+    }
+}
+```
+
+
+
 
 
 

From ee6bd7413c7a94135c760363c8a5f3fb6ccb0085 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Tue, 31 Aug 2021 10:46:18 +0800
Subject: [PATCH 13/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00056.=E5=90=88=E5=B9=B6?=
 =?UTF-8?q?=E5=8C=BA=E9=97=B4Java=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0056.合并区间.md | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/problems/0056.合并区间.md b/problems/0056.合并区间.md
index 2322951a..82ca29e6 100644
--- a/problems/0056.合并区间.md
+++ b/problems/0056.合并区间.md
@@ -157,6 +157,28 @@ class Solution {
     }
 }
 ```
+```java
+// 版本2
+class Solution {
+    public int[][] merge(int[][] intervals) {
+        LinkedList<int[]> res = new LinkedList<>();
+        Arrays.sort(intervals, (o1, o2) -> Integer.compare(o1[0], o2[0]));
+        res.add(intervals[0]);
+        for (int i = 1; i < intervals.length; i++) {
+            if (intervals[i][0] <= res.getLast()[1]) {
+                int start = res.getLast()[0];
+                int end = Math.max(intervals[i][1], res.getLast()[1]);
+                res.removeLast();
+                res.add(new int[]{start, end});
+            }
+            else {
+                res.add(intervals[i]);
+            }         
+        }
+        return res.toArray(new int[res.size()][]);
+    }
+}
+```
 
 Python：
 ```python

From 617499f4f8ba93078a27bdd244a3623e97056b51 Mon Sep 17 00:00:00 2001
From: wjjiang <48505670+Spongecaptain@users.noreply.github.com>
Date: Tue, 31 Aug 2021 11:10:14 +0800
Subject: [PATCH 14/57] =?UTF-8?q?Update=200115.=E4=B8=8D=E5=90=8C=E7=9A=84?=
 =?UTF-8?q?=E5=AD=90=E5=BA=8F=E5=88=97.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

添加 Go 语言版本
---
 problems/0115.不同的子序列.md | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/problems/0115.不同的子序列.md b/problems/0115.不同的子序列.md
index a5162ae0..908682dd 100644
--- a/problems/0115.不同的子序列.md
+++ b/problems/0115.不同的子序列.md
@@ -221,6 +221,30 @@ class SolutionDP2:
 ```
 
 Go：
+```go
+func numDistinct(s string, t string) int {
+    dp:= make([][]int,len(s)+1)
+    for i:=0;i<len(dp);i++{
+        dp[i] = make([]int,len(t)+1)
+    }
+    // 初始化
+    for i:=0;i<len(dp);i++{
+        dp[i][0] = 1
+    }
+    // dp[0][j] 为 0，默认值，因此不需要初始化
+    for i:=1;i<len(dp);i++{
+        for j:=1;j<len(dp[i]);j++{
+            if s[i-1] == t[j-1]{
+                dp[i][j] = dp[i-1][j-1] + dp[i-1][j]
+            }else{
+                dp[i][j] = dp[i-1][j]
+            }
+        }
+    }
+    return dp[len(dp)-1][len(dp[0])-1]
+}
+```
+
 
 Javascript:
 ```javascript

From d1815018ec228240e2007fd61544e89018b045bf Mon Sep 17 00:00:00 2001
From: wjjiang <48505670+Spongecaptain@users.noreply.github.com>
Date: Tue, 31 Aug 2021 11:40:29 +0800
Subject: [PATCH 15/57] =?UTF-8?q?Update=200583.=E4=B8=A4=E4=B8=AA=E5=AD=97?=
 =?UTF-8?q?=E7=AC=A6=E4=B8=B2=E7=9A=84=E5=88=A0=E9=99=A4=E6=93=8D=E4=BD=9C?=
 =?UTF-8?q?.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

添加 Go 版本
---
 .../0583.两个字符串的删除操作.md    | 32 ++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/problems/0583.两个字符串的删除操作.md b/problems/0583.两个字符串的删除操作.md
index 89a8f57c..91b07ca9 100644
--- a/problems/0583.两个字符串的删除操作.md
+++ b/problems/0583.两个字符串的删除操作.md
@@ -147,8 +147,38 @@ class Solution:
 ```
 
 Go：
+```go
+func minDistance(word1 string, word2 string) int {
+	dp := make([][]int, len(word1)+1)
+	for i := 0; i < len(dp); i++ {
+		dp[i] = make([]int, len(word2)+1)
+	}
+	//初始化
+	for i := 0; i < len(dp); i++ {
+		dp[i][0] = i
+	}
+	for j := 0; j < len(dp[0]); j++ {
+		dp[0][j] = j
+	}
+	for i := 1; i < len(dp); i++ {
+		for j := 1; j < len(dp[i]); j++ {
+			if word1[i-1] == word2[j-1] {
+				dp[i][j] = dp[i-1][j-1]
+			} else {
+				dp[i][j] = min(min(dp[i-1][j]+1, dp[i][j-1]+1), dp[i-1][j-1]+2)
+			}
+		}
+	}
+	return dp[len(dp)-1][len(dp[0])-1]
+}
 
-
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+```
 Javascript：
 ```javascript
 const minDistance = (word1, word2) => {

From 3e34ff114a3716d1548065348b5d3bc9d5f0199e Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Tue, 31 Aug 2021 12:22:13 +0800
Subject: [PATCH 16/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200077.=E7=BB=84?=
 =?UTF-8?q?=E5=90=88.md=20C=E8=AF=AD=E8=A8=80=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0077.组合.md | 53 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/problems/0077.组合.md b/problems/0077.组合.md
index 01d1a537..9b44b572 100644
--- a/problems/0077.组合.md
+++ b/problems/0077.组合.md
@@ -435,6 +435,59 @@ func backtrack(n,k,start int,track []int){
 }
 ```
 
+C:
+```c
+int* path;
+int pathTop;
+int** ans;
+int ansTop;
+
+void backtracking(int n, int k,int startIndex) {
+    //当path中元素个数为k个时，我们需要将path数组放入ans二维数组中
+    if(pathTop == k) {
+        //path数组为我们动态申请，若直接将其地址放入二维数组，path数组中的值会随着我们回溯而逐渐变化
+        //因此创建新的数组存储path中的值
+        int* temp = (int*)malloc(sizeof(int) * k);
+        int i;
+        for(i = 0; i < k; i++) {
+            temp[i] = path[i];
+        }
+        ans[ansTop++] = temp;
+        return ;
+    }
+
+    int j;
+    for(j = startIndex; j <=n ;j++) {
+        //将当前结点放入path数组
+        path[pathTop++] = j;
+        //进行递归
+        backtracking(n, k, j + 1);
+        //进行回溯，将数组最上层结点弹出
+        pathTop--;
+    }
+}
+
+int** combine(int n, int k, int* returnSize, int** returnColumnSizes){
+    //path数组存储符合条件的结果
+    path = (int*)malloc(sizeof(int) * k);
+    //ans二维数组存储符合条件的结果数组的集合。（数组足够大，避免极端情况）
+    ans = (int**)malloc(sizeof(int*) * 10000);
+    pathTop = ansTop = 0;
+
+    //回溯算法
+    backtracking(n, k, 1);
+    //最后的返回大小为ans数组大小
+    *returnSize = ansTop;
+    //returnColumnSizes数组存储ans二维数组对应下标中一维数组的长度（都为k）
+    *returnColumnSizes = (int*)malloc(sizeof(int) *(*returnSize));
+    int i;
+    for(i = 0; i < *returnSize; i++) {
+        (*returnColumnSizes)[i] = k;
+    }
+    //返回ans二维数组
+    return ans;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 14aee4922bc43138b18f10ce52eb521706749b7b Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Tue, 31 Aug 2021 12:32:20 +0800
Subject: [PATCH 17/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200027.=E7=A7=BB?=
 =?UTF-8?q?=E9=99=A4=E5=85=83=E7=B4=A0.md=20C=E8=AF=AD=E8=A8=80=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0027.移除元素.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/problems/0027.移除元素.md b/problems/0027.移除元素.md
index e3b75719..886ce4f2 100644
--- a/problems/0027.移除元素.md
+++ b/problems/0027.移除元素.md
@@ -246,6 +246,23 @@ func removeElement(_ nums: inout [Int], _ val: Int) -> Int {
 }
 ```
 
+C:
+```c
+int removeElement(int* nums, int numsSize, int val){
+    int slow = 0;
+    for(int fast = 0; fast < numsSize; fast++) {
+        //若快指针位置的元素不等于要删除的元素
+        if(nums[fast] != val) {
+            //将其挪到慢指针指向的位置，慢指针+1
+            nums[slow++] = nums[fast];
+        } 
+    }
+    //最后慢指针的大小就是新的数组的大小
+    return slow;
+}
+
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From d65afddc9189f1644237aca61cfb77f69dcb8292 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Tue, 31 Aug 2021 12:34:01 +0800
Subject: [PATCH 18/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200027.=E7=A7=BB?=
 =?UTF-8?q?=E9=99=A4=E5=85=83=E7=B4=A0.md=20C=E8=AF=AD=E8=A8=80=E6=B3=A8?=
 =?UTF-8?q?=E9=87=8A?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0027.移除元素.md | 1 -
 1 file changed, 1 deletion(-)

diff --git a/problems/0027.移除元素.md b/problems/0027.移除元素.md
index 886ce4f2..ff50d511 100644
--- a/problems/0027.移除元素.md
+++ b/problems/0027.移除元素.md
@@ -260,7 +260,6 @@ int removeElement(int* nums, int numsSize, int val){
     //最后慢指针的大小就是新的数组的大小
     return slow;
 }
-
 ```
 
 -----------------------

From 29876fbdee24c4cd3e10faefca2fd1f8a70664ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Tue, 31 Aug 2021 13:02:33 +0800
Subject: [PATCH 19/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=201002.=20=E6=9F=A5?=
 =?UTF-8?q?=E6=89=BE=E5=B8=B8=E7=94=A8=E5=AD=97=E7=AC=A6=20Swift=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/1002.查找常用字符.md | 41 +++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/problems/1002.查找常用字符.md b/problems/1002.查找常用字符.md
index f7d323aa..c0ca578e 100644
--- a/problems/1002.查找常用字符.md
+++ b/problems/1002.查找常用字符.md
@@ -268,6 +268,47 @@ func min(a,b int)int{
     return a
 }
 ```
+
+Swift：
+```swift
+func commonChars(_ words: [String]) -> [String] {
+    var res = [String]()
+    if words.count < 1 {
+        return res
+    }
+    let aUnicodeScalarValue = "a".unicodeScalars.first!.value
+    let lettersMaxCount = 26
+    // 用于统计所有字符串每个字母出现的 最小 频率
+    var hash = Array(repeating: 0, count: lettersMaxCount)
+    // 统计第一个字符串每个字母出现的次数
+    for unicodeScalar in words.first!.unicodeScalars {
+        hash[Int(unicodeScalar.value - aUnicodeScalarValue)] += 1
+    }
+    // 统计除第一个字符串每个字母出现的次数
+    for idx in 1 ..< words.count {
+        var hashOtherStr = Array(repeating: 0, count: lettersMaxCount)
+        for unicodeScalar in words[idx].unicodeScalars {
+            hashOtherStr[Int(unicodeScalar.value - aUnicodeScalarValue)] += 1
+        }
+        // 更新hash,保证hash里统计的字母为出现的最小频率
+        for k in 0 ..< lettersMaxCount {
+            hash[k] = min(hash[k], hashOtherStr[k])
+        }
+    }
+    // 将hash统计的字符次数，转成输出形式
+    for i in 0 ..< lettersMaxCount {
+        while hash[i] != 0 { // 注意这里是while，多个重复的字符
+            let currentUnicodeScalarValue: UInt32 = UInt32(i) + aUnicodeScalarValue
+            let currentUnicodeScalar: UnicodeScalar = UnicodeScalar(currentUnicodeScalarValue)!
+            let outputStr = String(currentUnicodeScalar) // UnicodeScalar -> String
+            res.append(outputStr)
+            hash[i] -= 1
+        }
+    }
+    return res
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From 55753bb5580e9a25a6af1e9cc10834156bf149b7 Mon Sep 17 00:00:00 2001
From: Asterisk <44215173+GHumorBS@users.noreply.github.com>
Date: Tue, 31 Aug 2021 14:30:39 +0800
Subject: [PATCH 20/57] =?UTF-8?q?Update=200232.=E7=94=A8=E6=A0=88=E5=AE=9E?=
 =?UTF-8?q?=E7=8E=B0=E9=98=9F=E5=88=97.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Python 更新：
1. 更新前版本的self.pop()语法错误
2. 更新后C++范例逻辑趋于统一
---
 problems/0232.用栈实现队列.md | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/problems/0232.用栈实现队列.md b/problems/0232.用栈实现队列.md
index a4a73603..9f6bb90f 100644
--- a/problems/0232.用栈实现队列.md
+++ b/problems/0232.用栈实现队列.md
@@ -205,33 +205,26 @@ class MyQueue:
 
     def pop(self) -> int:
         """
-        1. 检查如果out里面元素，则直接pop
-        2. 如果out没有元素，就把in里面的元素（除了第一个）依次pop后装进out里面
-        3. 直接把in剩下的元素pop出来，就是queue头部的
+        Removes the element from in front of queue and returns that element.
         """
-        if self.empty:
+        if self.empty():
             return None
         
         if self.stack_out:
             return self.stack_out.pop()
         else:
-            for i in range(1, len(self.stack_in)):
+            for i in range(len(self.stack_in)):
                 self.stack_out.append(self.stack_in.pop())
-            return self.stack_in.pop()
+            return self.stack_out.pop()
 
 
     def peek(self) -> int:
         """
-        1. 查out有没有元素，有就把最上面的返回
-        2. 如果out没有元素，就把in最下面的返回
+        Get the front element.
         """
-        if self.empty:
-            return None
-        
-        if self.stack_out:
-            return self.stack_out[-1]
-        else:
-            return self.stack_in[0]
+        ans = self.pop()
+        self.stack_out.append(ans)
+        return ans
 
 
     def empty(self) -> bool:

From f172c95e882e4eb8cc13636469588f81c5695bc4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Tue, 31 Aug 2021 14:36:45 +0800
Subject: [PATCH 21/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20=E7=AC=AC202?=
 =?UTF-8?q?=E9=A2=98.=20=E5=BF=AB=E4=B9=90=E6=95=B0=20Swift=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0202.快乐数.md | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/problems/0202.快乐数.md b/problems/0202.快乐数.md
index b9386a68..e6365c71 100644
--- a/problems/0202.快乐数.md
+++ b/problems/0202.快乐数.md
@@ -191,7 +191,37 @@ var isHappy = function(n) {
 };
 ```
 
-
+Swift：
+```swift
+// number 每个位置上的数字的平方和
+func getSum(_ number: Int) -> Int {
+    var sum = 0
+    var num = number
+    while num > 0 {
+        let temp = num % 10
+        sum += (temp * temp)
+        num /= 10
+    }
+    return sum
+}
+func isHappy(_ n: Int) -> Bool {
+    var set = Set<Int>()
+    var num = n
+    while true {
+        let sum = self.getSum(num)
+        if sum == 1 {
+            return true
+        }
+        // 如果这个sum曾经出现过，说明已经陷入了无限循环了
+        if set.contains(sum) {
+            return false
+        } else {
+            set.insert(sum)
+        }
+        num = sum
+    }
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 71a24c5dd88a48d518a3be11ab9b68785c5dc66a Mon Sep 17 00:00:00 2001
From: baici1 <249337001@qq.com>
Date: Tue, 31 Aug 2021 15:57:51 +0800
Subject: [PATCH 22/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0225.=20=E7=94=A8?=
 =?UTF-8?q?=E9=98=9F=E5=88=97=E5=AE=9E=E7=8E=B0=E6=A0=88=20go=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0225.用队列实现栈.md | 65 +++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/problems/0225.用队列实现栈.md b/problems/0225.用队列实现栈.md
index afa563e3..8d4db953 100644
--- a/problems/0225.用队列实现栈.md
+++ b/problems/0225.用队列实现栈.md
@@ -359,6 +359,71 @@ class MyStack:
 
 Go：
 
+```go
+type MyStack struct {
+    queue []int//创建一个队列
+}
+
+
+/** Initialize your data structure here. */
+func Constructor() MyStack {
+    return MyStack{   //初始化
+        queue:make([]int,0),
+    }
+}
+
+
+/** Push element x onto stack. */
+func (this *MyStack) Push(x int)  {
+    //添加元素
+    this.queue=append(this.queue,x)
+}
+
+
+/** Removes the element on top of the stack and returns that element. */
+func (this *MyStack) Pop() int {
+    n:=len(this.queue)-1//判断长度
+    for n!=0{ //除了最后一个，其余的都重新添加到队列里
+        val:=this.queue[0]
+        this.queue=this.queue[1:]
+        this.queue=append(this.queue,val)
+        n--
+    }
+    //弹出元素
+    val:=this.queue[0]
+    this.queue=this.queue[1:]
+    return val
+    
+}
+
+
+/** Get the top element. */
+func (this *MyStack) Top() int {
+    //利用Pop函数，弹出来的元素重新添加
+    val:=this.Pop()
+    this.queue=append(this.queue,val)
+    return val
+}
+
+
+/** Returns whether the stack is empty. */
+func (this *MyStack) Empty() bool {
+    return len(this.queue)==0
+}
+
+
+/**
+ * Your MyStack object will be instantiated and called as such:
+ * obj := Constructor();
+ * obj.Push(x);
+ * param_2 := obj.Pop();
+ * param_3 := obj.Top();
+ * param_4 := obj.Empty();
+ */
+```
+
+
+
 javaScript: 
 
 使用数组（push, shift）模拟队列

From 9d1983fd02c428babb8809706744caa06bf4e57b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Wed, 1 Sep 2021 14:45:25 +0800
Subject: [PATCH 23/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=201.=20=E4=B8=A4?=
 =?UTF-8?q?=E6=95=B0=E4=B9=8B=E5=92=8C=20Swift=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0001.两数之和.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/problems/0001.两数之和.md b/problems/0001.两数之和.md
index fd17af62..f12b5869 100644
--- a/problems/0001.两数之和.md
+++ b/problems/0001.两数之和.md
@@ -206,6 +206,23 @@ function twoSum(array $nums, int $target): array
 }
 ```
 
+Swift：
+```swift
+func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
+    var res = [Int]()
+    var dict = [Int : Int]()
+    for i in 0 ..< nums.count {
+        let other = target - nums[i]
+        if dict.keys.contains(other) {
+            res.append(i)
+            res.append(dict[other]!)
+            return res
+        }
+        dict[nums[i]] = i
+    }
+    return res
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 4926d659a7937c880e631c4cde4f017d7e3e193e Mon Sep 17 00:00:00 2001
From: YusenAi <59075298+Aitensa@users.noreply.github.com>
Date: Wed, 1 Sep 2021 16:39:46 +0800
Subject: [PATCH 24/57] =?UTF-8?q?Update=200714.=E4=B9=B0=E5=8D=96=E8=82=A1?=
 =?UTF-8?q?=E7=A5=A8=E7=9A=84=E6=9C=80=E4=BD=B3=E6=97=B6=E6=9C=BA=E5=90=AB?=
 =?UTF-8?q?=E6=89=8B=E7=BB=AD=E8=B4=B9=EF=BC=88=E5=8A=A8=E6=80=81=E8=A7=84?=
 =?UTF-8?q?=E5=88=92=EF=BC=89.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 ...�佳时机含手续费（动态规划）.md | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md b/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
index 50db8868..b854c65c 100644
--- a/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
+++ b/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
@@ -152,6 +152,24 @@ class Solution:
 ```
 
 Go：
+```Go
+func maxProfit(prices []int, fee int) int {
+    n := len(prices)
+    dp := make([][2]int, n)
+    dp[0][0] = -prices[0]
+    for i := 1; i < n; i++ {
+        dp[i][1] = max(dp[i-1][1], dp[i-1][0]+prices[i]-fee)
+        dp[i][0] = max(dp[i-1][0], dp[i-1][1]-prices[i])
+    }
+    return dp[n-1][1]
+}
+func max(a, b int) int {
+    if a > b {
+        return a
+    }
+    return b
+}
+```
 
 Javascript：
 ```javascript

From e6fdf1023336647471c122b68779e34a2ee2facd Mon Sep 17 00:00:00 2001
From: YusenAi <59075298+Aitensa@users.noreply.github.com>
Date: Wed, 1 Sep 2021 16:45:15 +0800
Subject: [PATCH 25/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200714.=E4=B9=B0?=
 =?UTF-8?q?=E5=8D=96=E8=82=A1=E7=A5=A8=E7=9A=84=E6=9C=80=E4=BD=B3=E6=97=B6?=
 =?UTF-8?q?=E6=9C=BA=E5=90=AB=E6=89=8B=E7=BB=AD=E8=B4=B9=EF=BC=88=E5=8A=A8?=
 =?UTF-8?q?=E6=80=81=E8=A7=84=E5=88=92=EF=BC=89.md=20Go=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 ....买卖股票的最佳时机含手续费（动态规划）.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md b/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
index b854c65c..7c54a2fe 100644
--- a/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
+++ b/problems/0714.买卖股票的最佳时机含手续费（动态规划）.md
@@ -163,6 +163,7 @@ func maxProfit(prices []int, fee int) int {
     }
     return dp[n-1][1]
 }
+
 func max(a, b int) int {
     if a > b {
         return a

From 325a09cee71a83261ba037f29eb27bb4f0b2522e Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 18:44:41 -0400
Subject: [PATCH 26/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00704=E4=BA=8C=E5=88=86?=
 =?UTF-8?q?=E6=9F=A5=E6=89=BEPHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0704.二分查找.md | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/problems/0704.二分查找.md b/problems/0704.二分查找.md
index 495f7367..f358d2be 100644
--- a/problems/0704.二分查找.md
+++ b/problems/0704.二分查找.md
@@ -478,6 +478,38 @@ int search(int* nums, int numsSize, int target){
 }
 ```
 
+**PHP:**
+```php
+// 左闭右闭区间
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer
+     */
+    function search($nums, $target) {
+        if (count($nums) == 0) {
+            return -1;
+        }
+        $left = 0;
+        $right = count($nums) - 1;
+        while ($left <= $right) {
+            $mid = floor(($left + $right) / 2);
+            if ($nums[$mid] == $target) {
+                return $mid;
+            }
+            if ($nums[$mid] > $target) {
+                $right = $mid - 1;
+            }
+            else {
+                $left = $mid + 1;
+            }
+        }
+        return -1;
+    }
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From 3441bced1289c183f9e05b005c1a67a4971014a2 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 18:56:34 -0400
Subject: [PATCH 27/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200027.=E7=A7=BB?=
 =?UTF-8?q?=E9=99=A4=E5=85=83=E7=B4=A0=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0027.移除元素.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/problems/0027.移除元素.md b/problems/0027.移除元素.md
index e3b75719..7976dce3 100644
--- a/problems/0027.移除元素.md
+++ b/problems/0027.移除元素.md
@@ -246,6 +246,31 @@ func removeElement(_ nums: inout [Int], _ val: Int) -> Int {
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $val
+     * @return Integer
+     */
+    function removeElement(&$nums, $val) {
+        if (count($nums) == 0) {
+            return 0;
+        }
+        // 快慢指针
+        $slow = 0;
+        for ($fast = 0; $fast < count($nums); $fast++) {
+            if ($nums[$fast] != $val) {
+                $nums[$slow] = $nums[$fast];
+                $slow++;
+            }
+        }
+        return $slow;
+    }
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From 484491f840566ad219ee1505f13e8de355a11429 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 19:02:40 -0400
Subject: [PATCH 28/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200977.=E6=9C=89?=
 =?UTF-8?q?=E5=BA=8F=E6=95=B0=E7=BB=84=E7=9A=84=E5=B9=B3=E6=96=B9=20PHP?=
 =?UTF-8?q?=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0977.有序数组的平方.md | 27 ++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/problems/0977.有序数组的平方.md b/problems/0977.有序数组的平方.md
index 13142853..250234e1 100644
--- a/problems/0977.有序数组的平方.md
+++ b/problems/0977.有序数组的平方.md
@@ -270,6 +270,33 @@ def sorted_squares(nums)
 end
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer[]
+     */
+    function sortedSquares($nums) {
+        $res = [];
+        for ($i = 0; $i < count($nums); $i++) {
+            $res[$i] = 0;
+        }
+        $k = count($nums) - 1;
+        for ($i = 0, $j = count($nums) - 1; $i <= $j; ) {
+            if ($nums[$i] ** 2 < $nums[$j] ** 2) {
+                $res[$k--] = $nums[$j] ** 2;
+                $j--;
+            }
+            else {
+                $res[$k--] = $nums[$i] ** 2;
+                $i++;
+            }
+        } 
+        return $res;
+    }
+}
+```
 
 
 -----------------------

From efda64220ff36302999fb24b3e850262363ef76b Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 19:03:48 -0400
Subject: [PATCH 29/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200977.=E6=9C=89?=
 =?UTF-8?q?=E5=BA=8F=E6=95=B0=E7=BB=84=E7=9A=84=E5=B9=B3=E6=96=B9=20PHP?=
 =?UTF-8?q?=E7=89=88=E6=9C=AC=E6=B3=A8=E9=87=8A?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0977.有序数组的平方.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/problems/0977.有序数组的平方.md b/problems/0977.有序数组的平方.md
index 250234e1..a10afbfb 100644
--- a/problems/0977.有序数组的平方.md
+++ b/problems/0977.有序数组的平方.md
@@ -278,6 +278,7 @@ class Solution {
      * @return Integer[]
      */
     function sortedSquares($nums) {
+        // 双指针法
         $res = [];
         for ($i = 0; $i < count($nums); $i++) {
             $res[$i] = 0;

From a6a8dc080647bfe243824a7990f346941f5aa128 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 19:05:54 -0400
Subject: [PATCH 30/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200209.=E9=95=BF?=
 =?UTF-8?q?=E5=BA=A6=E6=9C=80=E5=B0=8F=E7=9A=84=E5=AD=90=E6=95=B0=E7=BB=84?=
 =?UTF-8?q?=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0209.长度最小的子数组.md | 28 +++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/problems/0209.长度最小的子数组.md b/problems/0209.长度最小的子数组.md
index ceca8c87..7c3fd0e7 100644
--- a/problems/0209.长度最小的子数组.md
+++ b/problems/0209.长度最小的子数组.md
@@ -264,6 +264,34 @@ impl Solution {
 }
 ```
 
+PHP:
+```php
+// 双指针 - 滑动窗口
+class Solution {
+    /**
+     * @param Integer $target
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    function minSubArrayLen($target, $nums) {
+        if (count($nums) < 1) {
+            return 0;
+        }
+        $sum = 0;
+        $res = PHP_INT_MAX;
+        $left = 0;
+        for ($right = 0; $right < count($nums); $right++) {
+            $sum += $nums[$right];
+            while ($sum >= $target) {
+                $res = min($res, $right - $left + 1);
+                $sum -= $nums[$left];
+                $left++;
+            }
+        }
+        return $res == PHP_INT_MAX ? 0 : $res;
+    }
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From e8851b049069734f3f7c8b03ef5c8a2e698dd25b Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Wed, 1 Sep 2021 19:08:21 -0400
Subject: [PATCH 31/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200059.=E8=9E=BA?=
 =?UTF-8?q?=E6=97=8B=E7=9F=A9=E9=98=B5II=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0059.螺旋矩阵II.md | 42 +++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/problems/0059.螺旋矩阵II.md b/problems/0059.螺旋矩阵II.md
index 4231fb39..3dbc2a50 100644
--- a/problems/0059.螺旋矩阵II.md
+++ b/problems/0059.螺旋矩阵II.md
@@ -426,6 +426,48 @@ impl Solution {
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer[][]
+     */
+    function generateMatrix($n) {
+        // 初始化数组
+        $res = array_fill(0, $n, array_fill(0, $n, 0));
+        $mid = $loop = floor($n / 2);
+        $startX = $startY = 0;
+        $offset = 1;
+        $count = 1;
+        while ($loop > 0) {
+            $i = $startX;
+            $j = $startY;
+            for (; $j < $startY + $n - $offset; $j++) {
+                $res[$i][$j] = $count++;
+            }
+            for (; $i < $startX + $n - $offset; $i++) {
+                $res[$i][$j] = $count++;
+            }
+            for (; $j > $startY; $j--) {
+                $res[$i][$j] = $count++;
+            }
+            for (; $i > $startX; $i--) {
+                $res[$i][$j] = $count++;
+            }
+            $startX += 1;
+            $startY += 1;
+            $offset += 2;
+            $loop--;
+        }
+        if ($n % 2 == 1) {
+            $res[$mid][$mid] = $count;
+        }
+        return $res;
+    }
+}
+```
+
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From dd11a104a48b4d63e8c479670fc38e26f70cb802 Mon Sep 17 00:00:00 2001
From: martisss <2466632626@qq.com>
Date: Thu, 2 Sep 2021 11:27:27 +0800
Subject: [PATCH 32/57] =?UTF-8?q?=E5=A2=9E=E5=8A=A0530=E4=BA=8C=E5=8F=89?=
 =?UTF-8?q?=E6=90=9C=E7=B4=A2=E6=A0=91=E7=9A=84=E6=9C=80=E5=B0=8F=E7=BB=9D?=
 =?UTF-8?q?=E5=AF=B9=E5=B7=AE.md=20js=E9=80=92=E5=BD=92=E4=B8=8E=E8=BF=AD?=
 =?UTF-8?q?=E4=BB=A3=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../0530.二叉搜索树的最小绝对差.md | 43 ++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md
index 46f6b796..ae6719ec 100644
--- a/problems/0530.二叉搜索树的最小绝对差.md
+++ b/problems/0530.二叉搜索树的最小绝对差.md
@@ -265,7 +265,7 @@ func getMinimumDifference(root *TreeNode) int {
 ```
 
 ## JavaScript 
-
+递归 先转换为有序数组
 ```javascript
 /**
  * Definition for a binary tree node.
@@ -297,6 +297,47 @@ var getMinimumDifference = function (root) {
     return diff;
 };
 ```
+递归 在递归的过程中更新最小值
+```js
+var getMinimumDifference = function(root) {
+    let res = Infinity
+    let preNode = null
+    // 中序遍历
+    const inorder = (node) => {
+        if(!node) return
+        inorder(node.left)
+        // 更新res
+        if(preNode) res = Math.min(res, node.val - preNode.val)
+        // 记录前一个节点         
+        preNode = node
+        inorder(node.right)
+    }
+    inorder(root)
+    return res
+}
+```
+
+迭代  中序遍历
+```js
+var getMinimumDifference = function(root) {
+    let stack = []
+    let cur = root
+    let res = Infinity
+    let pre = null
+    while(cur || stack.length) {
+        if(cur) {
+            stack.push(cur)
+            cur = cur.left
+        } else {
+            cur = stack.pop()
+            if(pre) res = Math.min(res, cur.val - pre.val)
+            pre = cur
+            cur = cur.right
+        }
+    }
+    return res
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 6886111727e91ee5a616d9e1056a6be3447991a1 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Thu, 2 Sep 2021 12:17:45 +0800
Subject: [PATCH 33/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200077.=E7=BB=84?=
 =?UTF-8?q?=E5=90=88=E4=BC=98=E5=8C=96.md=20C=E8=AF=AD=E8=A8=80=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0077.组合优化.md | 51 +++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/problems/0077.组合优化.md b/problems/0077.组合优化.md
index 171023dd..136ceb34 100644
--- a/problems/0077.组合优化.md
+++ b/problems/0077.组合优化.md
@@ -242,8 +242,59 @@ var combine = function(n, k) {
 };
 ```
 
+C:
+```c
+int* path;
+int pathTop;
+int** ans;
+int ansTop;
 
+void backtracking(int n, int k,int startIndex) {
+    //当path中元素个数为k个时，我们需要将path数组放入ans二维数组中
+    if(pathTop == k) {
+        //path数组为我们动态申请，若直接将其地址放入二维数组，path数组中的值会随着我们回溯而逐渐变化
+        //因此创建新的数组存储path中的值
+        int* temp = (int*)malloc(sizeof(int) * k);
+        int i;
+        for(i = 0; i < k; i++) {
+            temp[i] = path[i];
+        }
+        ans[ansTop++] = temp;
+        return ;
+    }
 
+    int j;
+    for(j = startIndex; j <= n- (k - pathTop) + 1;j++) {
+        //将当前结点放入path数组
+        path[pathTop++] = j;
+        //进行递归
+        backtracking(n, k, j + 1);
+        //进行回溯，将数组最上层结点弹出
+        pathTop--;
+    }
+}
+
+int** combine(int n, int k, int* returnSize, int** returnColumnSizes){
+    //path数组存储符合条件的结果
+    path = (int*)malloc(sizeof(int) * k);
+    //ans二维数组存储符合条件的结果数组的集合。（数组足够大，避免极端情况）
+    ans = (int**)malloc(sizeof(int*) * 10000);
+    pathTop = ansTop = 0;
+
+    //回溯算法
+    backtracking(n, k, 1);
+    //最后的返回大小为ans数组大小
+    *returnSize = ansTop;
+    //returnColumnSizes数组存储ans二维数组对应下标中一维数组的长度（都为k）
+    *returnColumnSizes = (int*)malloc(sizeof(int) *(*returnSize));
+    int i;
+    for(i = 0; i < *returnSize; i++) {
+        (*returnColumnSizes)[i] = k;
+    }
+    //返回ans二维数组
+    return ans;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 8a35955a04594b22d6ea07af06188580a5c6c9f4 Mon Sep 17 00:00:00 2001
From: ArthurP <gpan20020205@gmail.com>
Date: Thu, 2 Sep 2021 12:33:00 +0800
Subject: [PATCH 34/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200977.=E6=9C=89?=
 =?UTF-8?q?=E5=BA=8F=E6=95=B0=E7=BB=84=E7=9A=84=E5=B9=B3=E6=96=B9.md=20C?=
 =?UTF-8?q?=E8=AF=AD=E8=A8=80=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0977.有序数组的平方.md | 31 ++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/problems/0977.有序数组的平方.md b/problems/0977.有序数组的平方.md
index 13142853..089884fc 100644
--- a/problems/0977.有序数组的平方.md
+++ b/problems/0977.有序数组的平方.md
@@ -270,7 +270,38 @@ def sorted_squares(nums)
 end
 ```
 
+C:
+```c
+int* sortedSquares(int* nums, int numsSize, int* returnSize){
+    //返回的数组大小就是原数组大小
+    *returnSize = numsSize;
+    //创建两个指针，right指向数组最后一位元素，left指向数组第一位元素
+    int right = numsSize - 1;
+    int left = 0;
 
+    //最后要返回的结果数组
+    int* ans = (int*)malloc(sizeof(int) * numsSize);
+    int index;
+    for(index = numsSize - 1; index >= 0; index--) {
+        //左指针指向元素的平方
+        int lSquare = nums[left] * nums[left];
+        //右指针指向元素的平方
+        int rSquare = nums[right] * nums[right];
+        //若左指针指向元素平方比右指针指向元素平方大，将左指针指向元素平方放入结果数组。左指针右移一位
+        if(lSquare > rSquare) {
+            ans[index] = lSquare;
+            left++;
+        } 
+        //若右指针指向元素平方比左指针指向元素平方大，将右指针指向元素平方放入结果数组。右指针左移一位
+        else {
+            ans[index] = rSquare;
+            right--;
+        }
+    }
+    //返回结果数组
+    return ans;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 34e8e4d5149159c9f95b63246e59219a930b78ea Mon Sep 17 00:00:00 2001
From: YusenAi <59075298+Aitensa@users.noreply.github.com>
Date: Thu, 2 Sep 2021 13:12:36 +0800
Subject: [PATCH 35/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200968.=E7=9B=91?=
 =?UTF-8?q?=E6=8E=A7=E4=BA=8C=E5=8F=89=E6=A0=91.md=20=20Go=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0968.监控二叉树.md | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/problems/0968.监控二叉树.md b/problems/0968.监控二叉树.md
index 737e92a0..a5fa71a7 100644
--- a/problems/0968.监控二叉树.md
+++ b/problems/0968.监控二叉树.md
@@ -368,7 +368,34 @@ class Solution:
         return result
 ```
 Go：
+```go
+const inf = math.MaxInt64 / 2
 
+func minCameraCover(root *TreeNode) int {
+    var dfs func(*TreeNode) (a, b, c int)
+    dfs = func(node *TreeNode) (a, b, c int) {
+        if node == nil {
+            return inf, 0, 0
+        }
+        lefta, leftb, leftc := dfs(node.Left)
+        righta, rightb, rightc := dfs(node.Right)
+        a = leftc + rightc + 1
+        b = min(a, min(lefta+rightb, righta+leftb))
+        c = min(a, leftb+rightb)
+        return
+    }
+    _, ans, _ := dfs(root)
+    return ans
+}
+
+func min(a, b int) int {
+    if a <= b {
+        return a
+    }
+    return b
+}
+
+```
 Javascript:
 ```Javascript
 var minCameraCover = function(root) {

From ac49e879e0c913a65e6a3955b066aafef1641bcd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Thu, 2 Sep 2021 13:29:07 +0800
Subject: [PATCH 36/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20=E7=AC=AC454?=
 =?UTF-8?q?=E9=A2=98.=E5=9B=9B=E6=95=B0=E7=9B=B8=E5=8A=A0II=20Swift?=
 =?UTF-8?q?=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0454.四数相加II.md | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/problems/0454.四数相加II.md b/problems/0454.四数相加II.md
index 4e61dc2f..1c3f45e7 100644
--- a/problems/0454.四数相加II.md
+++ b/problems/0454.四数相加II.md
@@ -220,8 +220,33 @@ var fourSumCount = function(nums1, nums2, nums3, nums4) {
 };
 ```
 
-
-
+Swift：
+```swift
+func fourSumCount(_ nums1: [Int], _ nums2: [Int], _ nums3: [Int], _ nums4: [Int]) -> Int {
+    // key:a+b的数值，value:a+b数值出现的次数
+    var map = [Int: Int]()
+    // 遍历nums1和nums2数组，统计两个数组元素之和，和出现的次数，放到map中
+    for i in 0 ..< nums1.count {
+        for j in 0 ..< nums2.count {
+            let sum1 = nums1[i] + nums2[j]
+            map[sum1] = (map[sum1] ?? 0) + 1
+        }
+    }
+    // 统计a+b+c+d = 0 出现的次数
+    var res = 0
+    // 在遍历大num3和num4数组，找到如果 0-(c+d) 在map中出现过的话，就把map中key对应的value也就是出现次数统计出来。
+    for i in 0 ..< nums3.count {
+        for j in 0 ..< nums4.count {
+            let sum2 = nums3[i] + nums4[j]
+            let other = 0 - sum2
+            if map.keys.contains(other) {
+                res += map[other]!
+            }
+        }
+    }
+    return res
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 186d4e4ca41d2de86e25a009bb89d454096e5405 Mon Sep 17 00:00:00 2001
From: Wen Liang <wenslife@outlook.com>
Date: Thu, 2 Sep 2021 14:06:04 +0800
Subject: [PATCH 37/57] =?UTF-8?q?=E4=BF=AE=E6=AD=A3=20=E4=BA=8C=E5=8F=89?=
 =?UTF-8?q?=E6=A0=91=E7=9A=84=E8=BF=AD=E4=BB=A3=E9=81=8D=E5=8E=86.md=20?=
 =?UTF-8?q?=E4=B8=AD=E7=9A=84=E6=8B=BC=E5=86=99=E9=94=99=E8=AF=AF=20?=
 =?UTF-8?q?=E8=B7=9F=E8=8A=82=E7=82=B9=20->=20=E6=A0=B9=E8=8A=82=E7=82=B9?=
 =?UTF-8?q?=20=E4=B8=8D=E6=83=B3=20=20=20->=20=E4=B8=8D=E5=83=8F?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/二叉树的迭代遍历.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/problems/二叉树的迭代遍历.md b/problems/二叉树的迭代遍历.md
index a1d65070..84363610 100644
--- a/problems/二叉树的迭代遍历.md
+++ b/problems/二叉树的迭代遍历.md
@@ -27,7 +27,7 @@
 
 我们先看一下前序遍历。
 
-前序遍历是中左右，每次先处理的是中间节点，那么先将跟节点放入栈中，然后将右孩子加入栈，再加入左孩子。
+前序遍历是中左右，每次先处理的是中间节点，那么先将根节点放入栈中，然后将右孩子加入栈，再加入左孩子。
 
 为什么要先加入 右孩子，再加入左孩子呢？ 因为这样出栈的时候才是中左右的顺序。
 
@@ -140,7 +140,7 @@ public:
 
 # 总结
 
-此时我们用迭代法写出了二叉树的前后中序遍历，大家可以看出前序和中序是完全两种代码风格，并不想递归写法那样代码稍做调整，就可以实现前后中序。
+此时我们用迭代法写出了二叉树的前后中序遍历，大家可以看出前序和中序是完全两种代码风格，并不像递归写法那样代码稍做调整，就可以实现前后中序。
 
 **这是因为前序遍历中访问节点（遍历节点）和处理节点（将元素放进result数组中）可以同步处理，但是中序就无法做到同步！**
 

From 6a6858b2e84f65ba24c684a76359b83337ff2955 Mon Sep 17 00:00:00 2001
From: baici1 <249337001@qq.com>
Date: Thu, 2 Sep 2021 15:44:01 +0800
Subject: [PATCH 38/57] =?UTF-8?q?=E5=A2=9E=E5=8A=A0=20347.=E5=89=8D=20K=20?=
 =?UTF-8?q?=E4=B8=AA=E9=AB=98=E9=A2=91=E5=85=83=E7=B4=A0=20go=20=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC=E4=B8=A4=E4=B8=AA=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0347.前K个高频元素.md | 73 ++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/problems/0347.前K个高频元素.md b/problems/0347.前K个高频元素.md
index 54be5cc4..6012e118 100644
--- a/problems/0347.前K个高频元素.md
+++ b/problems/0347.前K个高频元素.md
@@ -189,6 +189,79 @@ class Solution:
 
 Go：
 
+```go
+//方法一：小顶堆
+func topKFrequent(nums []int, k int) []int {
+    map_num:=map[int]int{}
+    //记录每个元素出现的次数
+    for _,item:=range nums{
+        map_num[item]++
+    }
+    h:=&IHeap{}
+    heap.Init(h)
+    //所有元素入堆，堆的长度为k
+    for key,value:=range map_num{
+        heap.Push(h,[2]int{key,value})
+        if h.Len()>k{
+            heap.Pop(h)
+        }
+    }
+    res:=make([]int,k)
+    //按顺序返回堆中的元素
+    for i:=0;i<k;i++{
+        res[k-i-1]=heap.Pop(h).([2]int)[0]
+    }
+    return res
+}
+
+//构建小顶堆
+type IHeap [][2]int
+
+func (h IHeap) Len()int {
+    return len(h)
+}
+
+func (h IHeap) Less (i,j int) bool {
+    return h[i][1]<h[j][1]
+}
+
+func (h IHeap) Swap(i,j int) {
+    h[i],h[j]=h[j],h[i]
+}
+
+func (h *IHeap) Push(x interface{}){
+    *h=append(*h,x.([2]int))
+}
+func (h *IHeap) Pop() interface{}{
+    old:=*h
+    n:=len(old)
+    x:=old[n-1]
+    *h=old[0:n-1]
+    return x
+}
+
+
+//方法二:利用O(logn)排序
+func topKFrequent(nums []int, k int) []int {
+    ans:=[]int{}
+    map_num:=map[int]int{}
+    for _,item:=range nums {
+        map_num[item]++
+    }
+    for key,_:=range map_num{
+        ans=append(ans,key)
+    }
+    //核心思想：排序
+    //可以不用包函数，自己实现快排
+    sort.Slice(ans,func (a,b int)bool{
+        return map_num[ans[a]]>map_num[ans[b]]
+    })
+    return ans[:k]
+}
+```
+
+
+
 
 javaScript:
 ```js

From 15e342e00b65b61bc3846f47b972fca01267bf4a Mon Sep 17 00:00:00 2001
From: Asterisk <44215173+GHumorBS@users.noreply.github.com>
Date: Thu, 2 Sep 2021 17:15:42 +0800
Subject: [PATCH 39/57] =?UTF-8?q?Update=200017.=E7=94=B5=E8=AF=9D=E5=8F=B7?=
 =?UTF-8?q?=E7=A0=81=E7=9A=84=E5=AD=97=E6=AF=8D=E7=BB=84=E5=90=88.md?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

self.s 语法纠正
---
 problems/0017.电话号码的字母组合.md | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/problems/0017.电话号码的字母组合.md b/problems/0017.电话号码的字母组合.md
index 1ebf6f49..dfd0e875 100644
--- a/problems/0017.电话号码的字母组合.md
+++ b/problems/0017.电话号码的字母组合.md
@@ -322,20 +322,20 @@ python3：
 ```py
 class Solution:
     def letterCombinations(self, digits: str) -> List[str]:
-        self.s = ""
         res = []
+        s = ""
         letterMap = ["","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"]
-        if len(digits) == 0: return res
-        def backtrack(digits,index):
+        if not len(digits): return res
+        def backtrack(digits,index, s):
             if index == len(digits):
-                return res.append(self.s)
+                return res.append(s)
             digit = int(digits[index])  #将index指向的数字转为int
             letters = letterMap[digit]  #取数字对应的字符集
             for i in range(len(letters)):
-                self.s += letters[i]
-                backtrack(digits,index + 1)  #递归，注意index+1，一下层要处理下一个数字
-                self.s = self.s[:-1]  #回溯
-        backtrack(digits,0)
+                s += letters[i]
+                backtrack(digits, index+1, s)  #递归，注意index+1，一下层要处理下一个数字
+                s = s[:-1]  #回溯
+        backtrack(digits, 0, s)
         return res
 ```
 

From f5a5cd882f3725cc56a95541bb738025e7b05d89 Mon Sep 17 00:00:00 2001
From: Wen Liang <wenslife@outlook.com>
Date: Thu, 2 Sep 2021 17:22:28 +0800
Subject: [PATCH 40/57] =?UTF-8?q?=E4=BC=98=E5=8C=96=200102.=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=A0=91=E7=9A=84=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86?=
 =?UTF-8?q?.md=20Python3=E8=A7=A3=E6=B3=95=20=E4=BB=BB=E4=BD=95=E5=9C=A8?=
 =?UTF-8?q?=20list=20=E5=A4=B4=E9=83=A8=E8=BF=9B=E8=A1=8C=E7=9A=84?=
 =?UTF-8?q?=E6=93=8D=E4=BD=9C=E9=83=BD=E4=BC=9A=E6=8D=9F=E5=A4=B1=E4=B8=80?=
 =?UTF-8?q?=E5=AE=9A=E6=80=A7=E8=83=BD=20=E5=9C=A8=20Python=20=E4=B8=AD?=
 =?UTF-8?q?=E5=BA=94=E8=AF=A5=E4=BD=BF=E7=94=A8=20collections.deque=20?=
 =?UTF-8?q?=E4=BD=9C=E4=B8=BA=E9=98=9F=E5=88=97=E7=9A=84=E6=95=B0=E6=8D=AE?=
 =?UTF-8?q?=E7=B1=BB=E5=9E=8B=20=E5=9C=A8=E8=AF=A5=E6=95=B0=E6=8D=AE?=
 =?UTF-8?q?=E7=B1=BB=E5=9E=8B=E5=B7=A6=E5=8F=B3=E4=B8=A4=E7=AB=AF=E8=BF=BD?=
 =?UTF-8?q?=E5=8A=A0=E5=92=8C=E5=BC=B9=E5=87=BA=E5=85=83=E7=B4=A0=E7=9A=84?=
 =?UTF-8?q?=E6=97=B6=E9=97=B4=E5=A4=8D=E6=9D=82=E5=BA=A6=E9=83=BD=E6=8E=A5?=
 =?UTF-8?q?=E8=BF=91O(1)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0102.二叉树的层序遍历.md | 37 +++++++++++++----------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index a57a92aa..07708e5a 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -87,26 +87,31 @@ public:
 
 python代码：
 
-```python
+```python3
 class Solution:
+    """二叉树层序遍历迭代解法"""
+
     def levelOrder(self, root: TreeNode) -> List[List[int]]:
+        results = []
         if not root:
-            return []
+            return results
+        
+        from collections import deque
+        que = deque([root])
+        
+        while que:
+            size = len(que)
+            result = []
+            for _ in range(size):
+                cur = que.popleft()
+                result.append(cur.val)
+                if cur.left:
+                    que.append(cur.left)
+                if cur.right:
+                    que.append(cur.right)
+            results.append(result)
 
-        queue = [root]
-        out_list = []
-
-        while queue:
-            length = len(queue)  
-            in_list = []
-            for _ in range(length):
-                curnode = queue.pop(0)  # （默认移除列表最后一个元素）这里需要移除队列最头上的那个
-                in_list.append(curnode.val)
-                if curnode.left: queue.append(curnode.left)
-                if curnode.right: queue.append(curnode.right)
-            out_list.append(in_list)
-
-        return out_list
+        return results
 ```
 
 java: 

From acd13fc7d81aae428ee7bfd735b9e06c593eee11 Mon Sep 17 00:00:00 2001
From: Wen <wenslife@outlook.com>
Date: Thu, 2 Sep 2021 20:55:02 +0800
Subject: [PATCH 41/57] =?UTF-8?q?=E4=BC=98=E5=8C=96=200102.=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=A0=91=E7=9A=84=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86?=
 =?UTF-8?q?.md=20=E4=B8=AD=E7=9A=84=20107.=E4=BA=8C=E5=8F=89=E6=A0=91?=
 =?UTF-8?q?=E7=9A=84=E5=B1=82=E6=AC=A1=E9=81=8D=E5=8E=86=20II=20Python3?=
 =?UTF-8?q?=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0102.二叉树的层序遍历.md | 40 +++++++++++------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index 07708e5a..a02cf997 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -279,29 +279,29 @@ python代码：
 
 ```python
 class Solution:
+    """二叉树层序遍历II迭代解法"""
+
     def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
+        results = []
         if not root:
-            return []
-        quene = [root]
-        out_list = []
+            return results
         
-        while quene:
-            in_list = []
-            for _ in range(len(quene)):
-                node = quene.pop(0)
-                in_list.append(node.val)
-                if node.left:
-                    quene.append(node.left)
-                if node.right:
-                    quene.append(node.right)
- 
-            out_list.append(in_list)
-    
-        out_list.reverse()
-        return out_list
-    
-# 执行用时：36 ms, 在所有 Python3 提交中击败了92.00%的用户
-# 内存消耗：15.2 MB, 在所有 Python3 提交中击败了63.76%的用户
+        from collections import deque
+        que = deque([root])
+        
+        while que:
+            result = []
+            for _ in range(len(que)):
+                cur = que.popleft()
+                result.append(cur.val)
+                if cur.left:
+                    que.append(cur.left)
+                if cur.right:
+                    que.append(cur.right)
+            results.append(result)
+
+        results.reverse()
+        return results
 ```
 
 Java：

From fde18e8fddd5e2686ab46157344b5b3bbdb3d715 Mon Sep 17 00:00:00 2001
From: Wen Liang <wenslife@outlook.com>
Date: Fri, 3 Sep 2021 08:36:36 +0800
Subject: [PATCH 42/57] =?UTF-8?q?=E4=BC=98=E5=8C=96=200102.=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=A0=91=E7=9A=84=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86?=
 =?UTF-8?q?.md=20=E4=B8=AD=E7=9A=84=20637.=E4=BA=8C=E5=8F=89=E6=A0=91?=
 =?UTF-8?q?=E7=9A=84=E5=B1=82=E5=B9=B3=E5=9D=87=E5=80=BC=20Python3?=
 =?UTF-8?q?=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0102.二叉树的层序遍历.md | 41 +++++++++++------------
 1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index 07708e5a..4a0f62e0 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -633,32 +633,29 @@ python代码：
 
 ```python
 class Solution:
+    """二叉树层平均值迭代解法"""
+
     def averageOfLevels(self, root: TreeNode) -> List[float]:
+        results = []
         if not root:
-            return []
+            return results
         
-        quene = deque([root])
-        out_list = []
-
-        while quene:
-            in_list = []
-
-            for _ in range(len(quene)):
-                node = quene.popleft()
-                in_list.append(node.val)
-                if node.left:
-                    quene.append(node.left)
-                if node.right:
-                    quene.append(node.right)
-
-            out_list.append(in_list)
-
-        out_list = map(lambda x: sum(x) / len(x), out_list)
-    
-        return out_list
+        from collections import deque
+        que = deque([root])
         
-# 执行用时：56 ms, 在所有 Python3 提交中击败了81.48%的用户
-# 内存消耗：17 MB, 在所有 Python3 提交中击败了89.68%的用户
+        while que:
+            size = len(que)
+            sum_ = 0
+            for _ in range(size):
+                cur = que.popleft()
+                sum_ += cur.val
+                if cur.left:
+                    que.append(cur.left)
+                if cur.right:
+                    que.append(cur.right)
+            results.append(sum_ / size)
+
+        return results
 ```
 
 java:

From 578e9908c5470016110e8668815871c9826ff248 Mon Sep 17 00:00:00 2001
From: Wen Liang <wenslife@outlook.com>
Date: Fri, 3 Sep 2021 09:24:10 +0800
Subject: [PATCH 43/57] =?UTF-8?q?=E4=BC=98=E5=8C=96=200102.=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=A0=91=E7=9A=84=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86?=
 =?UTF-8?q?.md=20=E4=B8=AD=E7=9A=84=20429.N=E5=8F=89=E6=A0=91=E7=9A=84?=
 =?UTF-8?q?=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86=20Python3=E8=A7=A3?=
 =?UTF-8?q?=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0102.二叉树的层序遍历.md | 58 +++++++----------------
 1 file changed, 17 insertions(+), 41 deletions(-)

diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index 4a0f62e0..c25dbda4 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -825,52 +825,28 @@ public:
 python代码：
 
 ```python
-
 class Solution:
+    """N叉树的层序遍历迭代法"""
+
     def levelOrder(self, root: 'Node') -> List[List[int]]:
+        results = []
         if not root:
-            return []
+            return results
         
-        quene = deque([root])
-        out_list = []
-
-        while quene:
-            in_list = []
-
-            for _ in range(len(quene)):
-                node = quene.popleft()
-                in_list.append(node.val)
-                if node.children:
-                    # 这个地方要用extend而不是append，我们看下面的例子：
-                    # In [18]: alist=[]
-                    # In [19]: alist.append([1,2,3])
-                    # In [20]: alist
-                    # Out[20]: [[1, 2, 3]]
-                    # In [21]: alist.extend([4,5,6])
-                    # In [22]: alist
-                    # Out[22]: [[1, 2, 3], 4, 5, 6]
-                    # 可以看到extend对要添加的list进行了一个解包操作
-                    # print(root.children)，可以得到children是一个包含
-                    # 孩子节点地址的list，我们使用for遍历quene的时候，
-                    # 希望quene是一个单层list，所以要用extend
-                    # 使用extend的情况，如果print(quene),结果是
-                    # deque([<__main__.Node object at 0x7f60763ae0a0>])
-				   # deque([<__main__.Node object at 0x7f607636e6d0>, <__main__.Node object at 0x7f607636e130>, <__main__.Node object at 0x7f607636e310>])
-				  # deque([<__main__.Node object at 0x7f607636e880>, <__main__.Node object at 0x7f607636ef10>])
-				  # 可以看到是单层list
-                    # 如果使用append，print(quene)的结果是
-                    # deque([<__main__.Node object at 0x7f18907530a0>])
-				  # deque([[<__main__.Node object at 0x7f18907136d0>, <__main__.Node object at 0x7f1890713130>, <__main__.Node object at 0x7f1890713310>]])
-				  # 可以看到是两层list，这样for的遍历就会报错
-                    
-                    quene.extend(node.children)
-                
-            out_list.append(in_list)
+        from collections import deque
+        que = deque([root])
         
-        return out_list
-    
-# 执行用时：60 ms, 在所有 Python3 提交中击败了76.99%的用户
-# 内存消耗：16.5 MB, 在所有 Python3 提交中击败了89.19%的用户
+        while que:
+            result = []
+            for _ in range(len(que)):
+                cur = que.popleft()
+                result.append(cur.val)
+                # cur.children 是 Node 对象组成的列表，也可能为 None
+                if cur.children:
+                    que.extend(cur.children)
+            results.append(result)
+
+        return results
 ```
 
 java:

From b4c61303477091f537714935db04bb973fbddf27 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:41:55 -0400
Subject: [PATCH 44/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200203.=E7=A7=BB?=
 =?UTF-8?q?=E9=99=A4=E9=93=BE=E8=A1=A8=E5=85=83=E7=B4=A0=20PHP=E7=89=88?=
 =?UTF-8?q?=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0203.移除链表元素.md | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/problems/0203.移除链表元素.md b/problems/0203.移除链表元素.md
index 555dad03..c4f187e8 100644
--- a/problems/0203.移除链表元素.md
+++ b/problems/0203.移除链表元素.md
@@ -331,8 +331,32 @@ func removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {
 }
 ```
 
-
-
+PHP:
+```php
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+ // 虚拟头+双指针
+func removeElements(head *ListNode, val int) *ListNode {
+    dummyHead := &ListNode{}
+    dummyHead.Next = head
+    pred := dummyHead
+    cur := head
+    for cur != nil {
+        if cur.Val == val {
+            pred.Next = cur.Next
+        } else {
+            pred = cur
+        }
+        cur = cur.Next
+    }
+    return dummyHead.Next
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From 68710ed0066d3b3d9cbece33d116fa7fa3b6ad73 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:47:00 -0400
Subject: [PATCH 45/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200242.=E6=9C=89?=
 =?UTF-8?q?=E6=95=88=E7=9A=84=E5=AD=97=E6=AF=8D=E5=BC=82=E4=BD=8D=E8=AF=8D?=
 =?UTF-8?q?=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0242.有效的字母异位词.md | 35 +++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/problems/0242.有效的字母异位词.md b/problems/0242.有效的字母异位词.md
index 1b6b3109..3416ac06 100644
--- a/problems/0242.有效的字母异位词.md
+++ b/problems/0242.有效的字母异位词.md
@@ -221,6 +221,41 @@ func isAnagram(_ s: String, _ t: String) -> Bool {
 }
 ```
 
+PHP：
+```php
+class Solution {
+    /**
+     * @param String $s
+     * @param String $t
+     * @return Boolean
+     */
+    function isAnagram($s, $t) {
+        if (strlen($s) != strlen($t)) {
+            return false;
+        }
+        $table = [];
+        for ($i = 0; $i < strlen($s); $i++) {
+            if (!isset($table[$s[$i]])) {
+                $table[$s[$i]] = 1;
+            } else {
+                $table[$s[$i]]++;
+            }
+            if (!isset($table[$t[$i]])) {
+                $table[$t[$i]] = -1;
+            } else {
+                $table[$t[$i]]--;
+            }
+        }
+        foreach ($table as $record) {
+            if ($record != 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+```
+
 ## 相关题目
 
 * 383.赎金信

From 4a78d79db07f72daee8ef0086830f5b8a947d517 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:48:46 -0400
Subject: [PATCH 46/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200349.=E4=B8=A4?=
 =?UTF-8?q?=E4=B8=AA=E6=95=B0=E7=BB=84=E7=9A=84=E4=BA=A4=E9=9B=86=20PHP?=
 =?UTF-8?q?=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0349.两个数组的交集.md | 29 ++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/problems/0349.两个数组的交集.md b/problems/0349.两个数组的交集.md
index 752eee51..0cbdf85f 100644
--- a/problems/0349.两个数组的交集.md
+++ b/problems/0349.两个数组的交集.md
@@ -209,6 +209,35 @@ func intersection(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums1
+     * @param Integer[] $nums2
+     * @return Integer[]
+     */
+    function intersection($nums1, $nums2) {
+        if (count($nums1) == 0 || count($nums2) == 0) {
+            return [];
+        }
+        $counts = [];
+        $res = [];
+        foreach ($nums1 as $num) {
+            $counts[$num] = 1;
+        }
+        foreach ($nums2 as $num) {
+            if (isset($counts[$num])) {
+                $res[] = $num;
+            }
+            unset($counts[$num]);
+        }
+        
+        return $res;
+    }
+}
+```
+
 ## 相关题目
 
 * 350.两个数组的交集 II

From 485f6a806a712356fb3112b8522149650bc2756c Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:49:37 -0400
Subject: [PATCH 47/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200202.=E5=BF=AB?=
 =?UTF-8?q?=E4=B9=90=E6=95=B0=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0202.快乐数.md | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/problems/0202.快乐数.md b/problems/0202.快乐数.md
index e6365c71..710c824d 100644
--- a/problems/0202.快乐数.md
+++ b/problems/0202.快乐数.md
@@ -223,6 +223,37 @@ func isHappy(_ n: Int) -> Bool {
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Boolean
+     */
+    function isHappy($n) {
+        // use a set to record sum
+        // whenever there is a duplicated, stop
+        // == 1 return true, else false
+        $table = [];
+        while ($n != 1 && !isset($table[$n])) {
+            $table[$n] = 1;
+            $n = self::getNextN($n);
+        }
+        return $n == 1;
+    }
+
+    function getNextN(int $n) {
+        $res = 0;
+        while ($n > 0) {
+            $temp = $n % 10;
+            $res += $temp * $temp;
+            $n = floor($n / 10);
+        }
+        return $res;
+    }
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From 7f7d1eed323080d1755140484f095b4deec7a08b Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:50:54 -0400
Subject: [PATCH 48/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200001.=E4=B8=A4?=
 =?UTF-8?q?=E6=95=B0=E4=B9=8B=E5=92=8C=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0001.两数之和.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/problems/0001.两数之和.md b/problems/0001.两数之和.md
index f12b5869..a6381eff 100644
--- a/problems/0001.两数之和.md
+++ b/problems/0001.两数之和.md
@@ -224,6 +224,31 @@ func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer[]
+     */
+    function twoSum($nums, $target) {
+        if (count($nums) == 0) {
+            return [];
+        }
+        $table = [];
+        for ($i = 0; $i < count($nums); $i++) {
+            $temp = $target - $nums[$i];
+            if (isset($table[$temp])) {
+                return [$table[$temp], $i];
+            }
+            $table[$nums[$i]] = $i;
+        }
+        return [];
+    }
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

From 80eb43f36d73826d8131b1febe95d8c33743083a Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:51:43 -0400
Subject: [PATCH 49/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200454.=E5=9B=9B?=
 =?UTF-8?q?=E6=95=B0=E7=9B=B8=E5=8A=A0II=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0454.四数相加II.md | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/problems/0454.四数相加II.md b/problems/0454.四数相加II.md
index 4e61dc2f..9fe01ad1 100644
--- a/problems/0454.四数相加II.md
+++ b/problems/0454.四数相加II.md
@@ -220,7 +220,37 @@ var fourSumCount = function(nums1, nums2, nums3, nums4) {
 };
 ```
 
-
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums1
+     * @param Integer[] $nums2
+     * @param Integer[] $nums3
+     * @param Integer[] $nums4
+     * @return Integer
+     */
+    function fourSumCount($nums1, $nums2, $nums3, $nums4) {
+        $map = [];
+        foreach ($nums1 as $n1) {
+            foreach ($nums2 as $n2) {
+                $temp = $n1 + $n2;
+                $map[$temp] = isset($map[$temp]) ? $map[$temp]+1 : 1;
+            }
+        }
+        $count = 0;
+        foreach ($nums3 as $n3) {
+            foreach ($nums4 as $n4) {
+                $temp = 0 - $n3 - $n4;
+                if (isset($map[$temp])) {
+                    $count += $map[$temp];
+                }
+            }
+        }
+        return $count;
+    }
+}
+```
 
 
 -----------------------

From 7f30649d46cb35f2ff175f0f1309ae58fe962de9 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:52:20 -0400
Subject: [PATCH 50/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200383.=E8=B5=8E?=
 =?UTF-8?q?=E9=87=91=E4=BF=A1=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0383.赎金信.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/problems/0383.赎金信.md b/problems/0383.赎金信.md
index 64503cef..32b0ff7f 100644
--- a/problems/0383.赎金信.md
+++ b/problems/0383.赎金信.md
@@ -266,6 +266,31 @@ var canConstruct = function(ransomNote, magazine) {
 };
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param String $ransomNote
+     * @param String $magazine
+     * @return Boolean
+     */
+    function canConstruct($ransomNote, $magazine) {
+        if (count($ransomNote) > count($magazine)) {
+            return false;
+        }
+        $map = [];
+        for ($i = 0; $i < strlen($magazine); $i++) {
+            $map[$magazine[$i]] = ($map[$magazine[$i]] ?? 0) + 1;
+        }
+        for ($i = 0; $i < strlen($ransomNote); $i++) {
+            if (!isset($map[$ransomNote[$i]]) || --$map[$ransomNote[$i]] < 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+```
 
 
 -----------------------

From e6975415370067128b8a625944fedec91728f4fc Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:53:36 -0400
Subject: [PATCH 51/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200015.=E4=B8=89?=
 =?UTF-8?q?=E6=95=B0=E4=B9=8B=E5=92=8C=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0015.三数之和.md | 40 +++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/problems/0015.三数之和.md b/problems/0015.三数之和.md
index 1adb2d24..adb9a113 100644
--- a/problems/0015.三数之和.md
+++ b/problems/0015.三数之和.md
@@ -393,6 +393,46 @@ function threeSum(array $nums): array
 }
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer[][]
+     */
+    function threeSum($nums) {
+        $res = [];
+        sort($nums);
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($nums[$i] > 0) {
+                return $res;
+            }
+            if ($i > 0 && $nums[$i] == $nums[$i - 1]) {
+                continue;
+            }
+            $left = $i + 1;
+            $right = count($nums) - 1;
+            while ($left < $right) {
+                $sum = $nums[$i] + $nums[$left] + $nums[$right];
+                if ($sum < 0) {
+                    $left++;
+                }
+                else if ($sum > 0) {
+                    $right--;
+                }
+                else {
+                    $res[] = [$nums[$i], $nums[$left], $nums[$right]];
+                    while ($left < $right && $nums[$left] == $nums[$left + 1]) $left++;
+                    while ($left < $right && $nums[$right] == $nums[$right - 1]) $right--;
+                    $left++;
+                    $right--;
+                }
+            }
+        }
+        return $res;
+    }
+}
+```
 
 
 -----------------------

From 3e1d341aea97d6f162606827b3e55151820fc299 Mon Sep 17 00:00:00 2001
From: nolanzzz <nolanwork131@gmail.com>
Date: Thu, 2 Sep 2021 23:54:21 -0400
Subject: [PATCH 52/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200018.=E5=9B=9B?=
 =?UTF-8?q?=E6=95=B0=E4=B9=8B=E5=92=8C=20PHP=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0018.四数之和.md | 43 +++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/problems/0018.四数之和.md b/problems/0018.四数之和.md
index 6af033b9..c81c5df7 100644
--- a/problems/0018.四数之和.md
+++ b/problems/0018.四数之和.md
@@ -310,6 +310,49 @@ var fourSum = function(nums, target) {
 };
 ```
 
+PHP:
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer[][]
+     */
+    function fourSum($nums, $target) {
+        $res = [];
+        sort($nums);
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($i > 0 && $nums[$i] == $nums[$i - 1]) {
+                continue;
+            }
+            for ($j = $i + 1; $j < count($nums); $j++) {
+                if ($j > $i + 1 && $nums[$j] == $nums[$j - 1]) {
+                    continue;
+                }
+                $left = $j + 1;
+                $right = count($nums) - 1;
+                while ($left < $right) {
+                    $sum = $nums[$i] + $nums[$j] + $nums[$left] + $nums[$right];
+                    if ($sum < $target) {
+                        $left++;
+                    }
+                    else if ($sum > $target) {
+                        $right--;
+                    }
+                    else {
+                        $res[] = [$nums[$i], $nums[$j], $nums[$left], $nums[$right]];
+                        while ($left < $right && $nums[$left] == $nums[$left+1]) $left++;
+                        while ($left < $right && $nums[$right] == $nums[$right-1]) $right--;
+                        $left++;
+                        $right--;
+                    }
+                }
+            }
+        }
+        return $res;
+    }
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

From ed1b1d2d39b080e7e45c2a92cb11e631f7ec5d94 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Fri, 3 Sep 2021 13:25:14 +0800
Subject: [PATCH 53/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20383.=20=E8=B5=8E?=
 =?UTF-8?q?=E9=87=91=E4=BF=A1=20Swift=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0383.赎金信.md | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/problems/0383.赎金信.md b/problems/0383.赎金信.md
index 64503cef..18b1de9b 100644
--- a/problems/0383.赎金信.md
+++ b/problems/0383.赎金信.md
@@ -266,6 +266,28 @@ var canConstruct = function(ransomNote, magazine) {
 };
 ```
 
+Swift：
+```swift
+func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
+    var record = Array(repeating: 0, count: 26);
+    let aUnicodeScalarValue = "a".unicodeScalars.first!.value
+    for unicodeScalar in magazine.unicodeScalars {
+        // 通过record 记录 magazine 里各个字符出现的次数
+        let idx: Int = Int(unicodeScalar.value - aUnicodeScalarValue)
+        record[idx] += 1
+    }
+    for unicodeScalar in ransomNote.unicodeScalars {
+        // 遍历 ransomNote,在record里对应的字符个数做 -- 操作
+        let idx: Int = Int(unicodeScalar.value - aUnicodeScalarValue)
+        record[idx] -= 1
+        // 如果小于零说明在magazine没有
+        if record[idx] < 0 {
+            return false
+        }
+    }
+    return true
+}
+```
 
 
 -----------------------

From bbd1b2e9ca58ae177f3d656752cd01a2ee15f7a2 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Fri, 3 Sep 2021 17:19:26 +0800
Subject: [PATCH 54/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00102.=E4=BA=8C=E5=8F=89?=
 =?UTF-8?q?=E6=A0=91=E7=9A=84=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86=E9=80=92?=
 =?UTF-8?q?=E5=BD=92=E8=A7=A3=E6=B3=95Python=E4=BB=A3=E7=A0=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0102.二叉树的层序遍历.md | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index a57a92aa..baec1229 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -88,6 +88,7 @@ public:
 python代码：
 
 ```python
+# 迭代法
 class Solution:
     def levelOrder(self, root: TreeNode) -> List[List[int]]:
         if not root:
@@ -108,7 +109,20 @@ class Solution:
 
         return out_list
 ```
-
+```python
+# 递归法
+class Solution:
+    def levelOrder(self, root: TreeNode) -> List[List[int]]:
+        res = []
+        def helper(root, depth):
+            if not root: return []
+            if len(res) == depth: res.append([]) # start the current depth
+            res[depth].append(root.val) # fulfil the current depth
+            if  root.left: helper(root.left, depth + 1) # process child nodes for the next depth
+            if  root.right: helper(root.right, depth + 1)
+        helper(root, 0)
+        return res
+```
 java: 
 
 ```Java

From 767168a8b0ec3f9cc2b31a76355e98d89d87f3ea Mon Sep 17 00:00:00 2001
From: martisss <2466632626@qq.com>
Date: Sat, 4 Sep 2021 10:58:23 +0800
Subject: [PATCH 55/57] =?UTF-8?q?=E4=BF=AE=E5=A4=8D355.=E5=88=86=E5=8F=91?=
 =?UTF-8?q?=E9=A5=BC=E5=B9=B2.md=20js=E4=BB=A3=E7=A0=81=E6=98=BE=E7=A4=BA?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0455.分发饼干.md | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/problems/0455.分发饼干.md b/problems/0455.分发饼干.md
index 1e1c4afe..8e20c402 100644
--- a/problems/0455.分发饼干.md
+++ b/problems/0455.分发饼干.md
@@ -197,11 +197,10 @@ func findContentChildren(g []int, s []int) int {
 
   return child
 }
-
+```
 
 Javascript:
-​```Javascript
-
+```
 var findContentChildren = function(g, s) {
     g = g.sort((a, b) => a - b)
     s = s.sort((a, b) => a - b)

From 659b34c22f171d011ce8b9e3a826954183c30315 Mon Sep 17 00:00:00 2001
From: ironartisan <ironerhalo@gmail.com>
Date: Sat, 4 Sep 2021 15:06:39 +0800
Subject: [PATCH 56/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00222.=E5=AE=8C=E5=85=A8?=
 =?UTF-8?q?=E4=BA=8C=E5=8F=89=E6=A0=91=E7=9A=84=E8=8A=82=E7=82=B9=E4=B8=AA?=
 =?UTF-8?q?=E6=95=B0=E8=BF=AD=E4=BB=A3=E8=A7=A3=E6=B3=95Java=E4=BB=A3?=
 =?UTF-8?q?=E7=A0=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../0222.完全二叉树的节点个数.md    | 22 ++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/problems/0222.完全二叉树的节点个数.md b/problems/0222.完全二叉树的节点个数.md
index 6268c447..13017f7f 100644
--- a/problems/0222.完全二叉树的节点个数.md
+++ b/problems/0222.完全二叉树的节点个数.md
@@ -204,7 +204,27 @@ class Solution {
     }
 }
 ```
-
+```java
+class Solution {
+    // 迭代法
+    public int countNodes(TreeNode root) {
+        if (root == null) return 0;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        int result = 0;
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            while (size -- > 0) {
+                TreeNode cur = queue.poll();
+                result++;
+                if (cur.left != null) queue.offer(cur.left);
+                if (cur.right != null) queue.offer(cur.right);
+            }
+        }
+        return result;
+    }
+}
+```
 ```java
 class Solution {
     /**

From b83cc1602a91c6d9ad3268904d17be42415d6938 Mon Sep 17 00:00:00 2001
From: ironartisan <54694467+ironartisan@users.noreply.github.com>
Date: Sun, 5 Sep 2021 10:27:23 +0800
Subject: [PATCH 57/57] =?UTF-8?q?=E6=B7=BB=E5=8A=A00404.=E5=B7=A6=E5=8F=B6?=
 =?UTF-8?q?=E5=AD=90=E4=B9=8B=E5=92=8C.md=E5=B1=82=E5=BA=8F=E8=BF=AD?=
 =?UTF-8?q?=E4=BB=A3=E8=A7=A3=E6=B3=95Java=E4=BB=A3=E7=A0=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0404.左叶子之和.md | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/problems/0404.左叶子之和.md b/problems/0404.左叶子之和.md
index 2b627b6c..c0eb7c8e 100644
--- a/problems/0404.左叶子之和.md
+++ b/problems/0404.左叶子之和.md
@@ -201,7 +201,31 @@ class Solution {
     }
 }
 ```
-
+```java
+// 层序遍历迭代法
+class Solution {
+    public int sumOfLeftLeaves(TreeNode root) {
+        int sum = 0;
+        if (root == null) return 0;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            while (size -- > 0) {
+                TreeNode node = queue.poll();
+                if (node.left != null) { // 左节点不为空
+                    queue.offer(node.left);
+                    if (node.left.left == null && node.left.right == null){ // 左叶子节点
+                        sum += node.left.val;
+                    }
+                }
+                if (node.right != null) queue.offer(node.right);
+            }
+        }
+        return sum;
+    }
+}
+```
 
 
 ## Python