Merge branch 'master' into master

problems/0015.三数之和.md

@@ -545,5 +545,64 @@ int** threeSum(int* nums, int numsSize, int* returnSize, int** returnColumnSizes
 }
 ```
 
+C#:
+```csharp
+public class Solution
+{
+    public IList<IList<int>> ThreeSum(int[] nums)
+    {
+        var result = new List<IList<int>>();
+
+        Array.Sort(nums);
+
+        for (int i = 0; i < nums.Length - 2; i++)
+        {
+            int n1 = nums[i];
+
+            if (n1 > 0)
+                break;
+
+            if (i > 0 && n1 == nums[i - 1])
+                continue;
+
+            int left = i + 1;
+            int right = nums.Length - 1;
+
+            while (left < right)
+            {
+                int n2 = nums[left];
+                int n3 = nums[right];
+                int sum = n1 + n2 + n3;
+
+                if (sum > 0)
+                {
+                    right--;
+                }
+                else if (sum < 0)
+                {
+                    left++;
+                }
+                else
+                {
+                    result.Add(new List<int> { n1, n2, n3 });
+
+                    while (left < right && nums[left] == n2)
+                    {
+                        left++;
+                    }
+
+                    while (left < right && nums[right] == n3)
+                    {
+                        right--;
+                    }
+                }
+            }
+        }
+
+        return result;
+    }
+}
+```
+
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0018.四数之和.md

@@ -445,5 +445,67 @@ func fourSum(_ nums: [Int], _ target: Int) -> [[Int]] {
 }
 ```
 
+C#:
+```csharp
+public class Solution
+{
+    public IList<IList<int>> FourSum(int[] nums, int target)
+    {
+        var result = new List<IList<int>>();
+
+        Array.Sort(nums);
+
+        for (int i = 0; i < nums.Length - 3; i++)
+        {
+            int n1 = nums[i];
+            if (i > 0 && n1 == nums[i - 1])
+                continue;
+
+            for (int j = i + 1; j < nums.Length - 2; j++)
+            {
+                int n2 = nums[j];
+                if (j > i + 1 && n2 == nums[j - 1])
+                    continue;
+
+                int left = j + 1;
+                int right = nums.Length - 1;
+
+                while (left < right)
+                {
+                    int n3 = nums[left];
+                    int n4 = nums[right];
+                    int sum = n1 + n2 + n3 + n4;
+
+                    if (sum > target)
+                    {
+                        right--;
+                    }
+                    else if (sum < target)
+                    {
+                        left++;
+                    }
+                    else
+                    {
+                        result.Add(new List<int> { n1, n2, n3, n4 });
+
+                        while (left < right && nums[left] == n3)
+                        {
+                            left++;
+                        }
+
+                        while (left < right && nums[right] == n4)
+                        {
+                            right--;
+                        }
+                    }
+                }
+            }
+        }
+
+        return result;
+    }
+}
+```
+
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0051.N皇后.md

@@ -346,70 +346,57 @@ class Solution {
 
 ### Go 
 ```Go
-import "strings"
+func solveNQueens(n int) [][]string {
-var res [][]string
+    var res [][]string
+	chessboard := make([][]string, n)
+	for i := 0; i < n; i++ {
+		chessboard[i] = make([]string, n)
+	}
+	for i := 0; i < n; i++ {
+		for j := 0; j < n; j++ {
+			chessboard[i][j] = "."
+		}
+	}
+	var backtrack func(int)
+	backtrack = func(row int) {
+		if row == n {
+			temp := make([]string, n)
+			for i, rowStr := range chessboard {
+				temp[i] = strings.Join(rowStr, "")
+			}
+			res = append(res, temp)
+			return
+		}
+		for i := 0; i < n; i++ {
+			if isValid(n, row, i, chessboard) {
+				chessboard[row][i] = "Q"
+				backtrack(row + 1)
+				chessboard[row][i] = "."
+			}
+		}
+	}
+	backtrack(0)
+	return res
+}
 
-func isValid(board [][]string, row, col int) (res bool){
+func isValid(n, row, col int, chessboard [][]string) bool {
-    n := len(board)
+	for i := 0; i < row; i++ {
-    for i:=0; i < row; i++ {
+		if chessboard[i][col] == "Q" {
-        if board[i][col] == "Q" {
 			return false
 		}
 	}
-    for i := 0; i < n; i++{
+	for i, j := row-1, col-1; i >= 0 && j >= 0; i, j = i-1, j-1 {
-        if board[row][i] == "Q" {
+		if chessboard[i][j] == "Q" {
 			return false
 		}
 	}
-
+	for i, j := row-1, col+1; i >= 0 && j < n; i, j = i-1, j+1 {
-    for i ,j := row, col; i >= 0 && j >=0 ; i, j = i - 1, j- 1{
+		if chessboard[i][j] == "Q" {
-        if board[i][j] == "Q"{
-            return false
-        }
-    }
-    for i, j := row, col; i >=0 && j < n; i,j = i-1, j+1 {
-        if board[i][j] == "Q" {
 			return false
 		}
 	}
 	return true
 }
-
-func backtrack(board [][]string, row int) {
-    size := len(board)
-    if row == size{
-        temp := make([]string, size)
-        for i := 0; i<size;i++{
-            temp[i] = strings.Join(board[i],"")
-        }
-        res =append(res,temp)
-        return 
-    }
-    for col := 0; col < size; col++ {
-        if !isValid(board, row, col){
-            continue
-        }
-        board[row][col] = "Q"
-        backtrack(board, row+1)
-        board[row][col] = "."
-    }
-}
-
-func solveNQueens(n int) [][]string {
-    res = [][]string{}
-    board := make([][]string, n)
-    for i := 0; i < n; i++{
-        board[i] = make([]string, n)
-    }
-    for i := 0; i < n; i++{
-        for j := 0; j<n;j++{
-            board[i][j] = "."
-        }
-    }
-    backtrack(board, 0)
-
-    return res
-}
 ```
 ### Javascript 
 ```Javascript

problems/0063.不同路径II.md

@@ -266,46 +266,33 @@ Go：
 
 ```go
 func uniquePathsWithObstacles(obstacleGrid [][]int) int {
-	m,n:= len(obstacleGrid),len(obstacleGrid[0])
+	m, n := len(obstacleGrid), len(obstacleGrid[0])
 	// 定义一个dp数组
-	dp := make([][]int,m)
+	dp := make([][]int, m)
-	for i,_ := range dp {
+	for i, _ := range dp {
-		dp[i] = make([]int,n)
+		dp[i] = make([]int, n)
 	}
-	// 初始化
+	// 初始化, 如果是障碍物, 后面的就都是0, 不用循环了
-	for i:=0;i<m;i++ {
+	for i := 0; i < m && obstacleGrid[i][0] == 0; i++ {
-		// 如果是障碍物, 后面的就都是0, 不用循环了
+		dp[i][0] = 1
-		if obstacleGrid[i][0] == 1 {
-			break
 	}
-		dp[i][0]=1
+	for i := 0; i < n && obstacleGrid[0][i] == 0; i++ {
-	}
+		dp[0][i] = 1
-	for i:=0;i<n;i++ {
-		if obstacleGrid[0][i] == 1 {
-			break
-		}
-		dp[0][i]=1
 	}
 	// dp数组推导过程
-	for i:=1;i<m;i++ {
+	for i := 1; i < m; i++ {
-		for j:=1;j<n;j++ {
+		for j := 1; j < n; j++ {
-			// 如果obstacleGrid[i][j]这个点是障碍物, 那么我们的dp[i][j]保持为0
+			// 如果obstacleGrid[i][j]这个点是障碍物, 那么dp[i][j]保持为0
 			if obstacleGrid[i][j] != 1 {
 				// 否则我们需要计算当前点可以到达的路径数
-				dp[i][j] = dp[i-1][j]+dp[i][j-1]
+				dp[i][j] = dp[i-1][j] + dp[i][j-1]
 			}
 		}
 	}
-	// debug遍历dp
-	//for i,_ := range dp {
-	//	for j,_ := range dp[i] {
-	//		fmt.Printf("%.2v,",dp[i][j])
-	//	}
-	//	fmt.Println()
-	//}
 	return dp[m-1][n-1]
 }
 
+
 ```
 
 Javascript

problems/0110.平衡二叉树.md

@@ -730,5 +730,33 @@ bool isBalanced(struct TreeNode* root){
 }
 ```
 
+## Swift:
+
+>递归
+```swift
+func isBalanced(_ root: TreeNode?) -> Bool {
+    // -1 已经不是平衡二叉树
+    return getHeight(root) == -1 ? false : true
+}
+func getHeight(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    let leftHeight = getHeight(root.left)
+    if leftHeight == -1 {
+        return -1
+    }
+    let rightHeight = getHeight(root.right)
+    if rightHeight == -1 {
+        return -1
+    }
+    if abs(leftHeight - rightHeight) > 1 {
+        return -1
+    } else {
+        return 1 + max(leftHeight, rightHeight)
+    }
+}
+```
+
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0151.翻转字符串里的单词.md

@@ -553,6 +553,65 @@ function reverse(strArr, start, end) {
 }
 ```
 
+TypeScript：
+
+```typescript
+function reverseWords(s: string): string {
+    /** Utils **/
+    // 删除多余空格, 如'   hello     world   ' => 'hello world'
+    function delExtraSpace(arr: string[]): void {
+        let left: number = 0,
+            right: number = 0,
+            length: number = arr.length;
+        while (right < length && arr[right] === ' ') {
+            right++;
+        }
+        while (right < length) {
+            if (arr[right] === ' ' && arr[right - 1] === ' ') {
+                right++;
+                continue;
+            }
+            arr[left++] = arr[right++];
+        }
+        if (arr[left - 1] === ' ') {
+            arr.length = left - 1;
+        } else {
+            arr.length = left;
+        }
+    }
+    // 翻转字符串，如：'hello' => 'olleh'
+    function reverseWords(strArr: string[], start: number, end: number) {
+        let temp: string;
+        while (start < end) {
+            temp = strArr[start];
+            strArr[start] = strArr[end];
+            strArr[end] = temp;
+            start++;
+            end--;
+        }
+    }
+
+    /** Main code **/
+    let strArr: string[] = s.split('');
+    delExtraSpace(strArr);
+    let length: number = strArr.length;
+    // 翻转整个字符串
+    reverseWords(strArr, 0, length - 1);
+    let start: number = 0,
+        end: number = 0;
+    while (start < length) {
+        end = start;
+        while (strArr[end] !== ' ' && end < length) {
+            end++;
+        }
+        // 翻转单个单词
+        reverseWords(strArr, start, end - 1);
+        start = end + 1;
+    }
+    return strArr.join('');
+};
+```
+
 Swift:
 
 ```swift

problems/0257.二叉树的所有路径.md

@@ -582,97 +582,70 @@ var binaryTreePaths = function(root) {
 ```
 
 Swift:
-
+> 递归/回溯
-递归法：
-
 ```swift
 func binaryTreePaths(_ root: TreeNode?) -> [String] {
-        var result = Array<String>()
+    var res = [String]()
-        var path = Array<Int>()
     guard let root = root else {
-            return result
+        return res
     }
-        traversal(root, &path, &result)
+    var path = [Int]()
-        return result
+    _binaryTreePaths(root, path: &path, res: &res)
+    return res
+}
+func _binaryTreePaths(_ root: TreeNode, path: inout [Int], res: inout [String]) {
+    path.append(root.val)
+    if root.left ==  nil && root.right == nil {
+        var str = ""
+        for i in 0 ..< path.count - 1 {
+            str.append("\(path[i])->")
         }
-    
+        str.append("\(path.last!)")
-    func traversal(_ cur: TreeNode, _ path: inout Array<Int>, _ result: inout Array<String>) {
+        res.append(str)
-        path.append(cur.val)
-        // 递归终止条件：到达叶子节点
-        if cur.left == nil && cur.right == nil {
-            var pathString = ""
-            // 处理 path 前面的元素
-            for i in 0..<path.count - 1 {
-                let value = path[i]
-                pathString += String(value)
-                pathString += "->"
-            }
-            // 处理 path 最后一个元素
-            if let lastValue = path.last {
-                pathString += String(lastValue)
-            }
-            // 将路径存到数组中
-            result.append(pathString)
         return
     }
-        
+    if let left = root.left {
-        // 空节点不进入递归
+        _binaryTreePaths(left, path: &path, res: &res)
-        if let leftNode = cur.left {
-            traversal(leftNode, &path, &result)
-            // 回溯
         path.removeLast()
     }
-        // 空节点不进入递归
+    if let right = root.right {
-        if let rightNode = cur.right {
+        _binaryTreePaths(right, path: &path, res: &res)
-            traversal(rightNode, &path, &result)
-            // 回溯
         path.removeLast()
     }
-    }
+}
 ```
 
-迭代法：
+> 迭代
-
 ```swift
 func binaryTreePaths(_ root: TreeNode?) -> [String] {
-        // 保存树的遍历节点
+    var res = [String]()
-        var treeStack = [TreeNode]()
-        // 保存遍历路径的节点
-        var pathStack = [String]()
-        // 保存最终路径集合
-        var result = [String]()
     guard let root = root else {
-            return result
+        return res
     }
-        treeStack.append(root)
+    var stackNode = [TreeNode]()
-        pathStack.append(String(root.val))
+    stackNode.append(root)
-        while !treeStack.isEmpty {
-            let node = treeStack.removeLast()
-            let path = pathStack.removeLast()
     
-            // 遇到叶子节点
+    var stackStr = [String]()
+    stackStr.append("\(root.val)")
+    
+    while !stackNode.isEmpty {
+        let node = stackNode.popLast()!
+        let str = stackStr.popLast()!
         if node.left == nil && node.right == nil {
-                result.append(path)
+            res.append(str)
         }
-            
+        if let left = node.left {
-            if let rightNode = node.right {
+            stackNode.append(left)
-                treeStack.append(rightNode)
+            stackStr.append("\(str)->\(left.val)")
-                let tmp = path + "->" + String(rightNode.val)
-                pathStack.append(tmp)
         }
-            
+        if let right = node.right {
-            if let leftNode = node.left {
+            stackNode.append(right)
-                treeStack.append(leftNode)
+            stackStr.append("\(str)->\(right.val)")
-                let tmp = path + "->" + String(leftNode.val)
-                pathStack.append(tmp)
         }
     }
-        
+    return res
-        return result
+}
-    }
 ```
 
-
-
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0344.反转字符串.md

@@ -253,6 +253,19 @@ void reverseString(char* s, int sSize){
 }
 ```
 
+C#：
+```csharp
+public class Solution
+{
+    public void ReverseString(char[] s)
+    {
+        for (int i = 0, j = s.Length - 1; i < j; i++, j--)
+        {
+            (s[i], s[j]) = (s[j], s[i]);
+        }
+    }
+}
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0494.目标和.md

@@ -289,7 +289,7 @@ func findTargetSumWays(nums []int, target int) int {
 	for _, v := range nums {
 		sum += v
 	}
-	if target > sum {
+	if abs(target) > sum {
 		return 0
 	}
 	if (sum+target)%2 == 1 {
@@ -311,49 +311,12 @@ func findTargetSumWays(nums []int, target int) int {
 	}
 	return dp[bag]
 }
-```
-> 更新版，上一个跑不通了，因为会存在bag 小于0的情况
 
-```go
+func abs(x int) int {
-func findTargetSumWays(nums []int, target int) int {
+	return int(math.Abs(float64(x)))
-    //先转化为数学问题
-    //a-b=target
-    //a+b=sum
-    //a=(target+sum)/2
-    //求出sum
-    var sum int
-    for _,value:=range nums{
-        sum+=value
-    }
-    //如果sum<target或者 sum+target不是偶数（因为a是int） 或者两者之和小于0了
-    if sum<target||(sum+target)%2==1||(sum+target)<0{
-        return 0
-    }
-    //开始dp初始化
-    dp:=make([][]int,len(nums)+1)
-    for i:=0;i<=len(nums);i++{
-        tmp:=make([]int,(target+sum)/2+1)//背包容量
-        dp[i]=tmp
-    }
-    dp[0][0]=1//当背包容量为0，且物品为0时，填满背包就1种方法
-    for i:=0;i<len(nums)+1;i++{
-        if i==0{
-            continue
-        }
-        for j:=0;j<(target+sum)/2+1;j++{
-            if nums[i-1]<=j{//如果背包装的下
-                dp[i][j]=dp[i-1][j]+dp[i-1][j-nums[i-1]]
-            }else{
-                dp[i][j]=dp[i-1][j]
-            }
-        }
-    }
-    return dp[len(nums)][(target+sum)/2]
 }
 ```
 
-
-
 Javascript：
 ```javascript
 const findTargetSumWays = (nums, target) => {

problems/0541.反转字符串II.md

@@ -294,9 +294,21 @@ func reverseStr(_ s: String, _ k: Int) -> String {
 }
 ```
 
-
+C#：
-
+```csharp
-
+public class Solution
+{
+    public string ReverseStr(string s, int k)
+    {
+        Span<char> span = s.ToCharArray().AsSpan();
+        for (int i = 0; i < span.Length; i += 2 * k)
+        {
+            span[i + k < span.Length ? i..(i + k) : i..].Reverse();
+        }
+        return span.ToString();
+    }
+}
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0844.比较含退格的字符串.md

@@ -205,6 +205,42 @@ class Solution:
         return self.get_string(s) == self.get_string(t)
         pass
 ```
+双指针
+```python
+class Solution:
+    def backspaceCompare(self, s: str, t: str) -> bool:
+        s_index, t_index = len(s) - 1, len(t) - 1
+        s_backspace, t_backspace = 0, 0 # 记录s,t的#数量
+        while s_index >= 0 or t_index >= 0: # 使用or，以防长度不一致
+            while s_index >= 0: # 从后向前，消除s的#
+                if s[s_index] == '#':
+                    s_index -= 1
+                    s_backspace += 1
+                else:
+                    if s_backspace > 0:
+                        s_index -= 1
+                        s_backspace -= 1
+                    else:
+                        break
+            while t_index >= 0: # 从后向前，消除t的#
+                if t[t_index] == '#':
+                    t_index -= 1
+                    t_backspace += 1
+                else:
+                    if t_backspace > 0:
+                        t_index -= 1
+                        t_backspace -= 1
+                    else:
+                        break
+            if s_index >= 0 and t_index >= 0: # 后半部分#消除完了，接下来比较当前位的值
+                if s[s_index] != t[t_index]:
+                    return False
+            elif s_index >= 0 or t_index >= 0: # 一个字符串找到了待比较的字符，另一个没有，返回False
+                return False
+            s_index -= 1
+            t_index -= 1
+        return True
+```
 
 ### Go 
 
@@ -226,6 +262,51 @@ func backspaceCompare(s string, t string) bool {
 	return getString(s) == getString(t)
 }
 
+```
+双指针
+```go
+func backspaceCompare(s string, t string) bool {
+    s_index, t_index := len(s) - 1, len(t) - 1
+    s_backspace, t_backspace := 0, 0 // 记录s,t的#数量
+    for s_index >= 0 || t_index >= 0 { // 使用or，以防长度不一致
+        for s_index >= 0 { // 从后向前，消除s的#
+            if s[s_index] == '#' {
+                s_index--
+                s_backspace++
+            } else {
+                if s_backspace > 0 {
+                    s_index--
+                    s_backspace--
+                } else {
+                    break
+                }
+            }            
+        }
+        for t_index >= 0 { // 从后向前，消除t的#
+            if t[t_index] == '#' {
+                t_index--
+                t_backspace++
+            } else {
+                if t_backspace > 0 {
+                    t_index--
+                    t_backspace--
+                } else {
+                    break
+                }
+            }            
+        }
+        if s_index >= 0 && t_index >= 0 { // 后半部分#消除完了，接下来比较当前位的值
+            if s[s_index] != t[t_index] {
+                return false
+            } 
+        } else if s_index >= 0 || t_index >= 0 { // 一个字符串找到了待比较的字符，另一个没有，返回false
+            return false
+        }            
+        s_index--
+        t_index--
+    }      
+    return true
+}
 ```
 
 ### JavaScript 

problems/剑指Offer58-II.左旋转字符串.md

@@ -209,6 +209,61 @@ var reverseLeftWords = function(s, n) {
 };
 ```
 
+版本二（在原字符串上操作）：
+
+```js
+/**
+ * @param {string} s
+ * @param {number} n
+ * @return {string}
+ */
+var reverseLeftWords = function (s, n) {
+    /** Utils */
+    function reverseWords(strArr, start, end) {
+        let temp;
+        while (start < end) {
+            temp = strArr[start];
+            strArr[start] = strArr[end];
+            strArr[end] = temp;
+            start++;
+            end--;
+        }
+    }
+    /** Main code */
+    let strArr = s.split('');
+    let length = strArr.length;
+    reverseWords(strArr, 0, length - 1);
+    reverseWords(strArr, 0, length - n - 1);
+    reverseWords(strArr, length - n, length - 1);
+    return strArr.join('');
+};
+```
+
+TypeScript：
+
+```typescript
+function reverseLeftWords(s: string, n: number): string {
+    /** Utils */
+    function reverseWords(strArr: string[], start: number, end: number): void {
+        let temp: string;
+        while (start < end) {
+            temp = strArr[start];
+            strArr[start] = strArr[end];
+            strArr[end] = temp;
+            start++;
+            end--;
+        }
+    }
+    /** Main code */
+    let strArr: string[] = s.split('');
+    let length: number = strArr.length;
+    reverseWords(strArr, 0, length - 1);
+    reverseWords(strArr, 0, length - n - 1);
+    reverseWords(strArr, length - n, length - 1);
+    return strArr.join('');
+};
+```
+
 Swift:
 
 ```swift