Merge branch 'youngyangyang04:master' into master

problems/0040.组合总和II.md

@@ -392,7 +392,66 @@ var combinationSum2 = function(candidates, target) {
     }
 };
 ```
+C:
+```c
+int* path;
+int pathTop;
+int** ans;
+int ansTop;
+//记录ans中每一个一维数组的大小
+int* length;
+int cmp(const void* a1, const void* a2) {
+    return *((int*)a1) - *((int*)a2);
+}
 
+void backTracking(int* candidates, int candidatesSize,  int target, int sum, int startIndex) {
+    if(sum >= target) {
+        //若sum等于target，复制当前path进入
+        if(sum == target) {
+            int* tempPath = (int*)malloc(sizeof(int) * pathTop);
+            int j;
+            for(j = 0; j < pathTop; j++) {
+                tempPath[j] = path[j];
+            }
+            length[ansTop] = pathTop;
+            ans[ansTop++] = tempPath;
+        }
+        return ;
+    }
+
+    int i;
+    for(i = startIndex; i < candidatesSize; i++) {
+        //对同一层树中使用过的元素跳过
+        if(i > startIndex && candidates[i] == candidates[i-1])
+            continue;
+        path[pathTop++] = candidates[i];
+        sum += candidates[i];
+        backTracking(candidates, candidatesSize, target, sum, i + 1);
+        //回溯
+        sum -= candidates[i];
+        pathTop--;
+    }
+}
+
+int** combinationSum2(int* candidates, int candidatesSize, int target, int* returnSize, int** returnColumnSizes){
+    path = (int*)malloc(sizeof(int) * 50);
+    ans = (int**)malloc(sizeof(int*) * 100);
+    length = (int*)malloc(sizeof(int) * 100);
+    pathTop = ansTop = 0;
+    //快速排序candidates，让相同元素挨到一起
+    qsort(candidates, candidatesSize, sizeof(int), cmp);
+
+    backTracking(candidates, candidatesSize, target, 0, 0);
+
+    *returnSize = ansTop;
+    *returnColumnSizes = (int*)malloc(sizeof(int) * ansTop);
+    int i;
+    for(i = 0; i < ansTop; i++) {
+        (*returnColumnSizes)[i] = length[i];
+    }
+    return ans;
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0257.二叉树的所有路径.md

@@ -408,25 +408,57 @@ class Solution {
 Python：
 ```Python
 class Solution:
+    """二叉树的所有路径 递归法"""
+
     def binaryTreePaths(self, root: TreeNode) -> List[str]:
-        path=[]
+        path, result = '', []
-        res=[]
+        self.traversal(root, path, result)
-        def backtrace(root, path):
+        return result
-            if not root:return 
+    
-            path.append(root.val)
+    def traversal(self, cur: TreeNode, path: List, result: List):
-            if (not root.left)and (not root.right):
+        path += str(cur.val)
-               res.append(path[:])
+        # 如果当前节点为叶子节点，添加路径到结果中
-            ways=[]
+        if not (cur.left or cur.right):
-            if root.left:ways.append(root.left)
+            result.append(path)
-            if root.right:ways.append(root.right)
+            return
-            for way in ways:
+            
-                backtrace(way,path)
+        if cur.left:
-                path.pop()
+            self.traversal(cur.left, path + '->', result)
-        backtrace(root,path)
+            
-        return ["->".join(list(map(str,i))) for i in res]
+        if cur.right:
+            self.traversal(cur.right, path + '->', result)
 
 ```
 
+```python
+from collections import deque
+
+
+class Solution:
+    """二叉树的所有路径 迭代法"""
+
+    def binaryTreePaths(self, root: TreeNode) -> List[str]:
+        # 题目中节点数至少为1
+        stack, path_st, result = deque([root]), deque(), []
+        path_st.append(str(root.val))
+
+        while stack:
+            cur = stack.pop()
+            path = path_st.pop()
+            # 如果当前节点为叶子节点，添加路径到结果中
+            if not (cur.left or cur.right):
+                result.append(path)
+            if cur.right:
+                stack.append(cur.right)
+                path_st.append(path + '->' + str(cur.right.val))
+            if cur.left:
+                stack.append(cur.left)
+                path_st.append(path + '->' + str(cur.left.val))
+
+        return result
+```
+
+
 Go：
 ```go
 func binaryTreePaths(root *TreeNode) []string {

problems/0494.目标和.md

@@ -321,7 +321,7 @@ const findTargetSumWays = (nums, target) => {
 
     const sum = nums.reduce((a, b) => a+b);
     
-    if(target > sum) {
+    if(Math.abs(target) > sum) {
         return 0;
     }
 

problems/0654.最大二叉树.md

@@ -258,16 +258,30 @@ class Solution {
 ## Python 
 
 ```python
-//递归法
 class Solution:
+    """最大二叉树 递归法"""
+
     def constructMaximumBinaryTree(self, nums: List[int]) -> TreeNode:
-        if not nums: return None   //终止条件
+        return self.traversal(nums, 0, len(nums))
-        root = TreeNode(max(nums))   //新建节点
+    
-        p = nums.index(root.val)   //找到最大值位置
+    def traversal(self, nums: List[int], begin: int, end: int) -> TreeNode:
-        if p > 0: //保证有左子树
+        # 列表长度为0时返回空节点
-            root.left = self.constructMaximumBinaryTree(nums[:p])   //递归
+        if begin == end:
-        if p < len(nums): //保证有右子树
+            return None
-            root.right = self.constructMaximumBinaryTree(nums[p+1:])  //递归
+        
+        # 找到最大的值和其对应的下标
+        max_index = begin
+        for i in range(begin, end):
+            if nums[i] > nums[max_index]:
+                max_index = i
+        
+        # 构建当前节点
+        root = TreeNode(nums[max_index])
+        
+        # 递归构建左右子树
+        root.left = self.traversal(nums, begin, max_index)
+        root.right = self.traversal(nums, max_index + 1, end)
+        
         return root
 ```
 

problems/为了绝杀编辑距离，卡尔做了三步铺垫.md

@@ -167,7 +167,33 @@ else {
 
 
 Java：
-
+```java
+class Solution {
+    public int minDistance(String word1, String word2) {
+        int m = word1.length();
+        int n = word2.length();
+        int[][] dp = new int[m+1][n+1];
+        for(int i = 1; i <= m; i++){
+            dp[i][0] = i;
+        }
+        for(int i = 1; i <= n; i++){
+            dp[0][i] = i;
+        }
+        for(int i = 1; i <= m; i++){
+            for(int j = 1; j <= n; j++){
+                int left = dp[i][j-1]+1;
+                int mid = dp[i-1][j-1];
+                int right = dp[i-1][j]+1;
+                if(word1.charAt(i-1) != word2.charAt(j-1)){
+                    mid ++;
+                }
+                dp[i][j] = Math.min(left,Math.min(mid,right));
+            }
+        }
+        return dp[m][n];
+    }
+}
+```
 
 Python：
 

problems/背包理论基础01背包-1.md

@@ -34,7 +34,7 @@ leetcode上没有纯01背包的问题，都是01背包应用方面的题目，
 
 ## 01 背包
 
-有N件物品和一个最多能被重量为W 的背包。第i件物品的重量是weight[i]，得到的价值是value[i] 。**每件物品只能用一次**，求解将哪些物品装入背包里物品价值总和最大。
+有N件物品和一个最多能背重量为W 的背包。第i件物品的重量是weight[i]，得到的价值是value[i] 。**每件物品只能用一次**，求解将哪些物品装入背包里物品价值总和最大。
 
 ![动态规划-背包问题](https://img-blog.csdnimg.cn/20210117175428387.jpg)