From 6f9eca871f56027c3ab598cd9603bfbc6f6bd33f Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 10:32:59 +0800 Subject: [PATCH 01/13] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20070=E7=88=AC?= =?UTF-8?q?=E6=A5=BC=E6=A2=AF=20Java=20=E7=89=88=E6=9C=AC?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0070.爬楼梯.md | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/problems/0070.爬楼梯.md b/problems/0070.爬楼梯.md index f0a08f99..286e088f 100644 --- a/problems/0070.爬楼梯.md +++ b/problems/0070.爬楼梯.md @@ -213,6 +213,28 @@ public: Java： +```java +// 常规方式 +public int climbStairs(int n) { + int[] dp = new int[n + 1]; + dp[0] = 1; + dp[1] = 1; + for (int i = 2; i <= n; i++) { + dp[i] = dp[i - 1] + dp[i - 2]; + } + return dp[n]; +} +// 用变量记录代替数组 +public int climbStairs(int n) { + int a = 0, b = 1, c = 0; // 默认需要1次 + for (int i = 1; i <= n; i++) { + c = a + b; // f(i - 1) + f(n - 2) + a = b; // 记录上一轮的值 + b = c; // 向后步进1个数 + } + return c; +} +``` Python： From 9ceecd50b679fd215c778f64c49baa4f83b8c5fb Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 10:51:53 +0800 Subject: [PATCH 02/13] =?UTF-8?q?0020=20=E6=9C=89=E6=95=88=E6=8B=AC?= =?UTF-8?q?=E5=8F=B7=E5=A2=9E=E5=8A=A0Java=E6=96=B0=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0020.有效的括号.md | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/problems/0020.有效的括号.md b/problems/0020.有效的括号.md index 77c6e10a..98cc7cd8 100644 --- a/problems/0020.有效的括号.md +++ b/problems/0020.有效的括号.md @@ -162,6 +162,33 @@ class Solution { return deque.isEmpty(); } } +// 方法2 +class Solution { + public boolean isValid(String s) { + + Stack stack = new Stack<>(); + Map map = new HashMap() { + { + put('}', '{'); + put(']', '['); + put(')', '('); + } + }; + + for (Character c : s.toCharArray()) { // 顺序读取字符 + if (!stack.isEmpty() && map.containsKey(c)) { // 是右括号 && 栈不为空 + if (stack.peek() == map.get(c)) { // 取其对应的左括号直接和栈顶比 + stack.pop(); // 相同则抵消，出栈 + } else { + return false; // 不同则直接返回 + } + } else { + stack.push(c); // 左括号，直接入栈 + } + } + return stack.isEmpty(); // 看左右是否抵消完 + } +} ``` Python： From 060f1eadb35507f4d8b9a51ae0eb65ac215fc5d4 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:02:29 +0800 Subject: [PATCH 03/13] =?UTF-8?q?0024=E4=B8=A4=E4=B8=A4=E4=BA=A4=E6=8D=A2?= =?UTF-8?q?=E9=93=BE=E8=A1=A8=E4=B8=AD=E7=9A=84=E8=8A=82=E7=82=B9=20?= =?UTF-8?q?=E6=B7=BB=E5=8A=A0Java=E5=AE=9E=E7=8E=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../0024.两两交换链表中的节点.md | 20 +++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/problems/0024.两两交换链表中的节点.md b/problems/0024.两两交换链表中的节点.md index 9f07b4f7..0cfa7fb9 100644 --- a/problems/0024.两两交换链表中的节点.md +++ b/problems/0024.两两交换链表中的节点.md @@ -86,7 +86,27 @@ public: Java： +```java +// 虚拟头结点 +class Solution { + public ListNode swapPairs(ListNode head) { + ListNode dummyNode = new ListNode(0); + dummyNode.next = head; + ListNode prev = dummyNode; + + while (prev.next != null && prev.next.next != null) { + ListNode temp = head.next.next; // 缓存 next + prev.next = head.next; // 将 prev 的 next 改为 head 的 next + head.next.next = head; // 将 head.next(prev.next) 的next，指向 head + head.next = temp; // 将head 的 next 接上缓存的temp + prev = head; // 步进1位 + head = head.next; // 步进1位 + } + return dummyNode.next; + } +} +``` Python： From 8dedebcc8da5b715e44e0d8ee2dbcceedcaeef11 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:10:47 +0800 Subject: [PATCH 04/13] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=2098=E9=AA=8C=E8=AF=81?= =?UTF-8?q?=E4=BA=8C=E5=8F=89=E6=90=9C=E7=B4=A2=E6=A0=91Java=E7=AE=80?= =?UTF-8?q?=E6=B4=81=E4=BB=A3=E7=A0=81?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0098.验证二叉搜索树.md | 29 ++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/problems/0098.验证二叉搜索树.md b/problems/0098.验证二叉搜索树.md index f246c21a..d8945eff 100644 --- a/problems/0098.验证二叉搜索树.md +++ b/problems/0098.验证二叉搜索树.md @@ -304,6 +304,35 @@ class Solution { return true; } } + +// 简洁实现·递归解法 +class Solution { + public boolean isValidBST(TreeNode root) { + return validBST(Long.MIN_VALUE, Long.MAX_VALUE, root); + } + boolean validBST(long lower, long upper, TreeNode root) { + if (root == null) return true; + if (root.val <= lower || root.val >= upper) return false; + return validBST(lower, root.val, root.left) && validBST(root.val, upper, root.right); + } +} +// 简洁实现·中序遍历 +class Solution { + private long prev = Long.MIN_VALUE; + public boolean isValidBST(TreeNode root) { + if (root == null) { + return true; + } + if (!isValidBST(root.left)) { + return false; + } + if (root.val <= prev) { // 不满足二叉搜索树条件 + return false; + } + prev = root.val; + return isValidBST(root.right); + } +} ``` Python： From b83f378bee5f954c7d64fcac44fac03fb0387cf5 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:19:14 +0800 Subject: [PATCH 05/13] =?UTF-8?q?=E5=A2=9E=E5=8A=A0=200112=E8=B7=AF?= =?UTF-8?q?=E5=BE=84=E5=92=8CJava=20=E7=AE=80=E6=B4=81=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0112.路径总和.md | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/problems/0112.路径总和.md b/problems/0112.路径总和.md index 1b75113e..ecbefd90 100644 --- a/problems/0112.路径总和.md +++ b/problems/0112.路径总和.md @@ -332,6 +332,19 @@ class Solution { } } +// LC112 简洁方法 +class Solution { + public boolean hasPathSum(TreeNode root, int targetSum) { + + if (root == null) return false; // 为空退出 + + // 叶子节点判断是否符合 + if (root.left == null && root.right == null) return root.val == targetSum; + + // 求两侧分支的路径和 + return hasPathSum(root.left, targetSum - root.val) || hasPathSum(root.right, targetSum - root.val); + } +} ``` Python： From b7836d951f518ba437ed69863bbb3cf5fcc75638 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:25:22 +0800 Subject: [PATCH 06/13] =?UTF-8?q?0121=E4=B9=B0=E5=8D=96=E8=82=A1=E7=A5=A8?= =?UTF-8?q?=E6=9C=80=E4=BD=B3=E6=97=B6=E6=9C=BA=E6=B7=BB=E5=8A=A0=20Java?= =?UTF-8?q?=20=E7=89=88=E6=9C=AC=E5=AE=9E=E7=8E=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0121.买卖股票的最佳时机.md | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/problems/0121.买卖股票的最佳时机.md b/problems/0121.买卖股票的最佳时机.md index 3d564892..a0b35090 100644 --- a/problems/0121.买卖股票的最佳时机.md +++ b/problems/0121.买卖股票的最佳时机.md @@ -198,7 +198,22 @@ public: Java： - +```java +class Solution { + public int maxProfit(int[] prices) { + int minprice = Integer.MAX_VALUE; + int maxprofit = 0; + for (int i = 0; i < prices.length; i++) { + if (prices[i] < minprice) { + minprice = prices[i]; + } else if (prices[i] - minprice > maxprofit) { + maxprofit = prices[i] - minprice; + } + } + return maxprofit; + } +} +``` Python： From ec61f2430d3ab09f8dc1c998514dfc1ca77ba0bb Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:30:14 +0800 Subject: [PATCH 07/13] =?UTF-8?q?0122=E4=B9=B0=E5=8D=96=E8=82=A1=E7=A5=A8?= =?UTF-8?q?=E6=9C=80=E4=BD=B3=E6=97=B6=E6=9C=BA2=E6=B7=BB=E5=8A=A0Java?= =?UTF-8?q?=E5=8A=A8=E6=80=81=E8=A7=84=E5=88=92=E5=AE=9E=E7=8E=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...票的最佳时机II（动态规划）.md | 27 +++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/problems/0122.买卖股票的最佳时机II（动态规划）.md b/problems/0122.买卖股票的最佳时机II（动态规划）.md index 3444ca73..c85272bc 100644 --- a/problems/0122.买卖股票的最佳时机II（动态规划）.md +++ b/problems/0122.买卖股票的最佳时机II（动态规划）.md @@ -133,7 +133,34 @@ public: Java： +```java +// 动态规划 +class Solution + public int maxProfit(int[] prices) { + int n = prices.length; + int[][] dp = new int[n][2]; + dp[0][0] = 0; + dp[0][1] = -prices[0]; + for (int i = 1; i < n; ++i) { + dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] + prices[i]); + dp[i][1] = Math.max(dp[i - 1][1], dp[i - 1][0] - prices[i]); + } + return dp[n - 1][0]; + } + public int maxProfit(int[] prices) { + int n = prices.length; + int dp0 = 0, dp1 = -prices[0]; + for (int i = 1; i < n; ++i) { + int newDp0 = Math.max(dp0, dp1 + prices[i]); + int newDp1 = Math.max(dp1, dp0 - prices[i]); + dp0 = newDp0; + dp1 = newDp1; + } + return dp0; + } +} +``` Python： From 92992f05904788e8249f142f2b3eb5b6ad1c5ec4 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:43:00 +0800 Subject: [PATCH 08/13] =?UTF-8?q?0198=20=E6=89=93=E5=AE=B6=E5=8A=AB?= =?UTF-8?q?=E8=88=8D=E6=B7=BB=E5=8A=A0=20Java=E5=AE=9E=E7=8E=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0198.打家劫舍.md | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/problems/0198.打家劫舍.md b/problems/0198.打家劫舍.md index c64648ad..649dd055 100644 --- a/problems/0198.打家劫舍.md +++ b/problems/0198.打家劫舍.md @@ -111,7 +111,24 @@ public: Java： +```Java +// 动态规划 +class Solution { + public int rob(int[] nums) { + if (nums == null || nums.length == 0) return 0; + if (nums.length == 1) return nums[0]; + int[] dp = new int[nums.length + 1]; + dp[0] = nums[0]; + dp[1] = Math.max(dp[0], nums[1]); + for (int i = 2; i < nums.length; i++) { + dp[i] = Math.max(dp[i - 1], dp[i - 2] + nums[i]); + } + + return dp[nums.length - 1]; + } +} +``` Python： From 430d46749408f0d59bcce006c26f49a1c84fe04e Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:47:15 +0800 Subject: [PATCH 09/13] =?UTF-8?q?Update=200213.=E6=89=93=E5=AE=B6=E5=8A=AB?= =?UTF-8?q?=E8=88=8DII.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0213.打家劫舍II.md | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/problems/0213.打家劫舍II.md b/problems/0213.打家劫舍II.md index 55e71bc0..fc58a065 100644 --- a/problems/0213.打家劫舍II.md +++ b/problems/0213.打家劫舍II.md @@ -98,7 +98,28 @@ public: Java： +```Java +class Solution { + public int rob(int[] nums) { + if (nums == null || nums.length == 0) + return 0; + int len = nums.length; + if (len == 1) + return nums[0]; + return Math.max(robAction(nums, 0, len - 1), robAction(nums, 1, len)); + } + int robAction(int[] nums, int start, int end) { + int x = 0, y = 0, z = 0; + for (int i = start; i < end; i++) { + y = z; + z = Math.max(y, x + nums[i]); + x = y; + } + return z; + } +} +``` Python： From 335c4adcdfdf7e5d2a20c2a42bd0070b1356a24a Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:55:37 +0800 Subject: [PATCH 10/13] =?UTF-8?q?Update=200300.=E6=9C=80=E9=95=BF=E4=B8=8A?= =?UTF-8?q?=E5=8D=87=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 --- problems/0300.最长上升子序列.md | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/problems/0300.最长上升子序列.md b/problems/0300.最长上升子序列.md index 2bc5cf9c..1cdc48b9 100644 --- a/problems/0300.最长上升子序列.md +++ b/problems/0300.最长上升子序列.md @@ -110,7 +110,26 @@ public: Java： - +```Java +class Solution { + public int lengthOfLIS(int[] nums) { + int[] dp = new int[nums.length]; + Arrays.fill(dp, 1); + for (int i = 0; i < dp.length; i++) { + for (int j = 0; j < i; j++) { + if (nums[i] > nums[j]) { + dp[i] = Math.max(dp[i], dp[j] + 1); + } + } + } + int res = 0; + for (int i = 0; i < dp.length; i++) { + res = Math.max(res, dp[i]); + } + return res; + } +} +``` Python： From d4e756ba6f7d23db9b474562e6c5899237290c4b Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 11:59:55 +0800 Subject: [PATCH 11/13] =?UTF-8?q?Update=200337.=E6=89=93=E5=AE=B6=E5=8A=AB?= =?UTF-8?q?=E8=88=8DIII.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0337.打家劫舍III.md | 65 ++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) diff --git a/problems/0337.打家劫舍III.md b/problems/0337.打家劫舍III.md index 50b06e22..20eea817 100644 --- a/problems/0337.打家劫舍III.md +++ b/problems/0337.打家劫舍III.md @@ -218,7 +218,72 @@ public: Java： +```Java +class Solution { + // 1.递归去偷，超时 + public int rob(TreeNode root) { + if (root == null) + return 0; + int money = root.val; + if (root.left != null) { + money += rob(root.left.left) + rob(root.left.right); + } + if (root.right != null) { + money += rob(root.right.left) + rob(root.right.right); + } + return Math.max(money, rob(root.left) + rob(root.right)); + } + // 2.递归去偷，记录状态 + // 执行用时：3 ms , 在所有 Java 提交中击败了 56.24% 的用户 + public int rob1(TreeNode root) { + Map memo = new HashMap<>(); + return robAction(root, memo); + } + + int robAction(TreeNode root, Map memo) { + if (root == null) + return 0; + if (memo.containsKey(root)) + return memo.get(root); + int money = root.val; + if (root.left != null) { + money += robAction(root.left.left, memo) + robAction(root.left.right, memo); + } + if (root.right != null) { + money += robAction(root.right.left, memo) + robAction(root.right.right, memo); + } + int res = Math.max(money, robAction(root.left, memo) + robAction(root.right, memo)); + memo.put(root, res); + return res; + } + + // 3.状态标记递归 + // 执行用时：0 ms , 在所有 Java 提交中击败了 100% 的用户 + // 不偷：Max(左孩子不偷，左孩子偷) + Max(又孩子不偷，右孩子偷) + // root[0] = Math.max(rob(root.left)[0], rob(root.left)[1]) + + // Math.max(rob(root.right)[0], rob(root.right)[1]) + // 偷：左孩子不偷+ 右孩子不偷 + 当前节点偷 + // root[1] = rob(root.left)[0] + rob(root.right)[0] + root.val; + public int rob3(TreeNode root) { + int[] res = robAction1(root); + return Math.max(res[0], res[1]); + } + + int[] robAction1(TreeNode root) { + int res[] = new int[2]; + if (root == null) + return res; + + int[] left = robAction1(root.left); + int[] right = robAction1(root.right); + + res[0] = Math.max(left[0], left[1]) + Math.max(right[0], right[1]); + res[1] = root.val + left[0] + right[0]; + return res; + } +} +``` Python： From 1a962286b8c4829b1378b8442f2be07adf59c6db Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 12:02:59 +0800 Subject: [PATCH 12/13] =?UTF-8?q?Update=200509.=E6=96=90=E6=B3=A2=E9=82=A3?= =?UTF-8?q?=E5=A5=91=E6=95=B0.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0509.斐波那契数.md | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/problems/0509.斐波那契数.md b/problems/0509.斐波那契数.md index 8537ed8b..8be11312 100644 --- a/problems/0509.斐波那契数.md +++ b/problems/0509.斐波那契数.md @@ -171,7 +171,20 @@ public: Java： - +```Java +class Solution { + public int fib(int n) { + if (n < 2) return n; + int a = 0, b = 1, c = 0; + for (int i = 1; i < n; i++) { + c = a + b; + a = b; + b = c; + } + return c; + } +} +``` Python： From a560255502699162a4b1ca667f4bd91aad17ced2 Mon Sep 17 00:00:00 2001 From: zhenzi Date: Sat, 15 May 2021 12:11:00 +0800 Subject: [PATCH 13/13] =?UTF-8?q?Update=20=E4=BA=8C=E5=8F=89=E6=A0=91?= =?UTF-8?q?=E7=9A=84=E9=80=92=E5=BD=92=E9=81=8D=E5=8E=86.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/二叉树的递归遍历.md | 52 ++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) diff --git a/problems/二叉树的递归遍历.md b/problems/二叉树的递归遍历.md index 02d4b060..e8cf0bdd 100644 --- a/problems/二叉树的递归遍历.md +++ b/problems/二叉树的递归遍历.md @@ -115,7 +115,59 @@ void traversal(TreeNode* cur, vector& vec) { Java： +```Java +// 前序遍历·递归·LC144_二叉树的前序遍历 +class Solution { + ArrayList preOrderReverse(TreeNode root) { + ArrayList result = new ArrayList(); + preOrder(root, result); + return result; + } + void preOrder(TreeNode root, ArrayList result) { + if (root == null) { + return; + } + result.add(root.val); // 注意这一句 + preOrder(root.left, result); + preOrder(root.right, result); + } +} +// 中序遍历·递归·LC94_二叉树的中序遍历 +class Solution { + public List inorderTraversal(TreeNode root) { + List res = new ArrayList<>(); + inorder(root, res); + return res; + } + + void inorder(TreeNode root, List list) { + if (root == null) { + return; + } + inorder(root.left, list); + list.add(root.val); // 注意这一句 + inorder(root.right, list); + } +} +// 后序遍历·递归·LC145_二叉树的后序遍历 +class Solution { + public List postorderTraversal(TreeNode root) { + List res = new ArrayList<>(); + postorder(root, res); + return res; + } + + void postorder(TreeNode root, List list) { + if (root == null) { + return; + } + postorder(root.left, list); + postorder(root.right, list); + list.add(root.val); // 注意这一句 + } +} +``` Python：