Merge branch 'master' of https://github.com/youngyangyang04/leetcode

problems/0096.不同的二叉搜索树.md

@@ -211,6 +211,23 @@ func numTrees(n int)int{
 }
 ```
 
+Javascript：
+```Javascript
+const numTrees =(n) => {
+    let dp = new Array(n+1).fill(0);
+    dp[0] = 1;
+    dp[1] = 1;
+
+    for(let i = 2; i <= n; i++) {
+        for(let j = 1; j <= i; j++) {
+            dp[i] += dp[j-1] * dp[i-j];
+        }
+    }
+
+    return dp[n];
+};
+```
+
 
 
 -----------------------

problems/0108.将有序数组转换为二叉搜索树.md

@@ -209,6 +209,8 @@ public:
 
 
 Java：
+
+递归: 左闭右开 [left,right)
 ```Java
 class Solution {
     public TreeNode sortedArrayToBST(int[] nums) {
@@ -232,6 +234,75 @@ class Solution {
 
 ```
 
+递归: 左闭右闭 [left,right]
+```java
+class Solution {
+	public TreeNode sortedArrayToBST(int[] nums) {
+		TreeNode root = traversal(nums, 0, nums.length - 1);
+		return root;
+	}
+
+	// 左闭右闭区间[left, right)
+	private TreeNode traversal(int[] nums, int left, int right) {
+		if (left > right) return null;
+
+		int mid = left + ((right - left) >> 1);
+		TreeNode root = new TreeNode(nums[mid]);
+		root.left = traversal(nums, left, mid - 1);
+		root.right = traversal(nums, mid + 1, right);
+		return root;
+	}
+}
+```
+迭代: 左闭右闭 [left,right]
+```java
+class Solution {
+	public TreeNode sortedArrayToBST(int[] nums) {
+		if (nums.length == 0) return null;
+
+		//根节点初始化
+		TreeNode root = new TreeNode(-1);
+		Queue<TreeNode> nodeQueue = new LinkedList<>();
+		Queue<Integer> leftQueue = new LinkedList<>();
+		Queue<Integer> rightQueue = new LinkedList<>();
+
+		// 根节点入队列
+		nodeQueue.offer(root);
+		// 0为左区间下表初始位置
+		leftQueue.offer(0);
+		// nums.size() - 1为右区间下表初始位置
+		rightQueue.offer(nums.length - 1);
+
+		while (!nodeQueue.isEmpty()) {
+			TreeNode currNode = nodeQueue.poll();
+			int left = leftQueue.poll();
+			int right = rightQueue.poll();
+			int mid = left + ((right - left) >> 1);
+
+			// 将mid对应的元素给中间节点
+			currNode.val = nums[mid];
+
+			// 处理左区间
+			if (left <= mid - 1) {
+				currNode.left = new TreeNode(-1);
+				nodeQueue.offer(currNode.left);
+				leftQueue.offer(left);
+				rightQueue.offer(mid - 1);
+			}
+
+			// 处理右区间
+			if (right >= mid + 1) {
+				currNode.right = new TreeNode(-1);
+				nodeQueue.offer(currNode.right);
+				leftQueue.offer(mid + 1);
+				rightQueue.offer(right);
+			}
+		}
+		return root;
+	}
+}
+```
+
 Python：
 ```python3
 # Definition for a binary tree node.
@@ -279,6 +350,36 @@ func sortedArrayToBST(nums []int) *TreeNode {
 }
 ```
 
+JavaScript版本
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {number[]} nums
+ * @return {TreeNode}
+ */
+var sortedArrayToBST = function (nums) {
+    const buildTree = (Arr, left, right) => {
+        if (left > right)
+            return null;
+
+        let mid = Math.floor(left + (right - left) / 2);
+
+        let root = new TreeNode(Arr[mid]);
+        root.left = buildTree(Arr, left, mid - 1);
+        root.right = buildTree(Arr, mid + 1, right);
+        return root;
+    }
+    return buildTree(nums, 0, nums.length - 1);
+};
+```
 
 
 

problems/0115.不同的子序列.md

@@ -186,6 +186,40 @@ class Solution:
         return dp[-1][-1]
 ```
 
+Python3:
+```python
+class SolutionDP2:
+    """
+    既然dp[i]只用到dp[i - 1]的状态，
+    我们可以通过缓存dp[i - 1]的状态来对dp进行压缩，
+    减少空间复杂度。
+    （原理等同同于滚动数组）
+    """
+    
+    def numDistinct(self, s: str, t: str) -> int:
+        n1, n2 = len(s), len(t)
+        if n1 < n2:
+            return 0
+
+        dp = [0 for _ in range(n2 + 1)]
+        dp[0] = 1
+
+        for i in range(1, n1 + 1):
+            # 必须深拷贝
+            # 不然prev[i]和dp[i]是同一个地址的引用
+            prev = dp.copy()
+            # 剪枝，保证s的长度大于等于t
+            # 因为对于任意i，i > n1, dp[i] = 0
+            # 没必要跟新状态。 
+            end = i if i < n2 else n2
+            for j in range(1, end + 1):
+                if s[i - 1] == t[j - 1]:
+                    dp[j] = prev[j - 1] + prev[j]
+                else:
+                    dp[j] = prev[j]
+        return dp[-1]
+```
+
 Go：
 
 

problems/0216.组合总和III.md

@@ -227,6 +227,44 @@ public:
 
 
 Java：
+
+模板方法
+```java
+class Solution {
+	List<List<Integer>> result = new ArrayList<>();
+	LinkedList<Integer> path = new LinkedList<>();
+
+	public List<List<Integer>> combinationSum3(int k, int n) {
+		backTracking(n, k, 1, 0);
+		return result;
+	}
+
+	private void backTracking(int targetSum, int k, int startIndex, int sum) {
+		// 减枝
+		if (sum > targetSum) {
+			return;
+		}
+
+		if (path.size() == k) {
+			if (sum == targetSum) result.add(new ArrayList<>(path));
+			return;
+		}
+		
+		// 减枝 9 - (k - path.size()) + 1
+		for (int i = startIndex; i <= 9 - (k - path.size()) + 1; i++) {
+			path.add(i);
+			sum += i;
+			backTracking(targetSum, k, i + 1, sum);
+			//回溯
+			path.removeLast();
+			//回溯
+			sum -= i;
+		}
+	}
+}
+```
+
+其他方法
 ```java
 class Solution {
     List<List<Integer>> res = new ArrayList<>();

problems/0494.目标和.md

@@ -306,6 +306,36 @@ func findTargetSumWays(nums []int, target int) int {
 }
 ```
 
+Javascript：
+```javascript
+const findTargetSumWays = (nums, target) => {
+
+    const sum = nums.reduce((a, b) => a+b);
+    
+    if(target > sum) {
+        return 0;
+    }
+
+    if((target + sum) % 2) {
+        return 0;
+    }
+
+    const halfSum = (target + sum) / 2;
+    nums.sort((a, b) => a - b);
+
+    let dp = new Array(halfSum+1).fill(0);
+    dp[0] = 1;
+
+    for(let i = 0; i < nums.length; i++) {
+        for(let j = halfSum; j >= nums[i]; j--) {
+            dp[j] += dp[j - nums[i]];
+        }
+    }
+
+    return dp[halfSum];
+};
+```
+
 
 
 -----------------------

problems/0538.把二叉搜索树转换为累加树.md

@@ -239,7 +239,70 @@ func RightMLeft(root *TreeNode,sum *int) *TreeNode {
 }
 ```
 
+JavaScript版本
 
+> 递归
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var convertBST = function(root) {
+    let pre = 0;
+    const ReverseInOrder = (cur) => {
+        if(cur) {
+            ReverseInOrder(cur.right);
+            cur.val += pre;
+            pre = cur.val;
+            ReverseInOrder(cur.left);
+        }
+    }
+    ReverseInOrder(root);
+    return root;
+};
+```
+
+> 迭代
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var convertBST = function (root) {
+    let pre = 0;
+    let cur = root;
+    let stack = [];
+    while (cur !== null || stack.length !== 0) {
+        while (cur !== null) {
+            stack.push(cur);
+            cur = cur.right;
+        }
+        cur = stack.pop();
+        cur.val += pre;
+        pre = cur.val;
+        cur = cur.left;
+    }
+    return root;
+};
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0617.合并二叉树.md

@@ -319,7 +319,7 @@ Python：
 #         self.val = val
 #         self.left = left
 #         self.right = right
-//递归法*前序遍历
+# 递归法*前序遍历
 class Solution:
     def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
         if not root1: return root2  // 如果t1为空，合并之后就应该是t2
@@ -328,6 +328,32 @@ class Solution:
         root1.left = self.mergeTrees(root1.left , root2.left)  //左
         root1.right = self.mergeTrees(root1.right , root2.right)  //右
         return root1  //root1修改了结构和数值
+
+# 迭代法-覆盖原来的树      
+class Solution:
+    def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
+        if not root1: return root2
+        if not root2: return root1
+        # 迭代,将树2覆盖到树1
+        queue1 = [root1]
+        queue2 = [root2]
+        root = root1
+        while queue1 and queue2:
+            root1 = queue1.pop(0)
+            root2 = queue2.pop(0)
+            root1.val += root2.val
+            if not root1.left: # 如果树1左儿子不存在，则覆盖后树1的左儿子为树2的左儿子
+                root1.left = root2.left
+            elif root1.left and root2.left:
+                queue1.append(root1.left)
+                queue2.append(root2.left)
+
+            if not root1.right: # 同理，处理右儿子
+                root1.right = root2.right
+            elif root1.right and root2.right:
+                queue1.append(root1.right)
+                queue2.append(root2.right)
+        return root
 ```
 
 Go：

problems/动态规划-股票问题总结篇.md

@@ -375,12 +375,6 @@ p[i][3] = dp[i - 1][2];
 
 综上分析，递推代码如下：
 
-```C++
-dp[i][0] = max(dp[i - 1][0], max(dp[i - 1][3], dp[i - 1][1]) - prices[i];
-dp[i][1] = max(dp[i - 1][1], dp[i - 1][3]);
-dp[i][2] = dp[i - 1][0] + prices[i];
-dp[i][3] = dp[i - 1][2];
-```
 ```C++
 dp[i][0] = max(dp[i - 1][0], max(dp[i - 1][3]- prices[i], dp[i - 1][1]) - prices[i];
 dp[i][1] = max(dp[i - 1][1], dp[i - 1][3]);

problems/周总结/20201003二叉树周末总结.md

@@ -40,9 +40,8 @@ public:
         return isSame;
 
     }
-    bool isSymmetric(TreeNode* root) {
-        if (root == NULL) return true;
-        return compare(root->left, root->right);
+    bool isSymmetric(TreeNode* p, TreeNode* q) {
+        return compare(p, q);
     }
 };
 ```