添加java 和 python版本

README.md

@@ -390,6 +390,7 @@
 * [分割回文串（对应力扣题目：131.分割回文串)](https://www.bilibili.com/video/BV1c54y1e7k6)
 * [二叉树理论基础](https://www.bilibili.com/video/BV1Hy4y1t7ij)
 * [二叉树的递归遍历](https://www.bilibili.com/video/BV1Wh411S7xt)
+* [二叉树的非递归遍历（一）](https://www.bilibili.com/video/BV15f4y1W7i2)
 
 （持续更新中....）
 

problems/0051.N皇后.md

@@ -231,3 +231,124 @@ public:
 大家可以在仔细体会体会！
 
 
+## 其他语言补充
+
+
+Python：
+
+```python
+class Solution:
+    def solveNQueens(self, n: int) -> List[List[str]]:
+        if not n: return []
+        board = [['.'] * n for _ in range(n)]
+        res = []
+        def isVaild(board,row, col):
+            #判断同一列是否冲突
+            for i in range(len(board)):
+                if board[i][col] == 'Q':
+                    return False
+            # 判断左上角是否冲突
+            i = row -1
+            j = col -1
+            while i>=0 and j>=0:
+                if board[i][j] == 'Q':
+                    return False
+                i -= 1
+                j -= 1
+            # 判断右上角是否冲突
+            i = row - 1
+            j = col + 1
+            while i>=0 and j < len(board):
+                if board[i][j] == 'Q':
+                    return False
+                i -= 1
+                j += 1
+            return True
+
+        def backtracking(board, row, n):
+            # 如果走到最后一行，说明已经找到一个解
+            if row == n:
+                temp_res = []
+                for temp in board:
+                    temp_str = "".join(temp)
+                    temp_res.append(temp_str)
+                res.append(temp_res)
+            for col in range(n):
+                if not isVaild(board, row, col):
+                    continue
+                board[row][col] = 'Q'
+                backtracking(board, row+1, n)
+                board[row][col] = '.'
+        backtracking(board, 0, n)
+        return res
+```
+
+Java：
+
+```java
+class Solution {
+    List<List<String>> res = new ArrayList<>();
+
+    public List<List<String>> solveNQueens(int n) {
+        char[][] chessboard = new char[n][n];
+        for (char[] c : chessboard) {
+            Arrays.fill(c, '.');
+        }
+        backTrack(n, 0, chessboard);
+        return res;
+    }
+
+
+    public void backTrack(int n, int row, char[][] chessboard) {
+        if (row == n) {
+            res.add(Array2List(chessboard));
+            return;
+        }
+
+        for (int col = 0;col < n; ++col) {
+            if (isValid (row, col, n, chessboard)) {
+                chessboard[row][col] = 'Q';
+                backTrack(n, row+1, chessboard);
+                chessboard[row][col] = '.';
+            }
+        }
+
+    }
+
+
+    public List Array2List(char[][] chessboard) {
+        List<String> list = new ArrayList<>();
+
+        for (char[] c : chessboard) {
+            list.add(String.copyValueOf(c));
+        }
+        return list;
+    }
+
+
+    public boolean isValid(int row, int col, int n, char[][] chessboard) {
+        // 检查列
+        for (int i=0; i<n; ++i) {
+            if (chessboard[i][col] == 'Q') {
+                return false;
+            }
+        }
+
+        // 检查45度对角线
+        for (int i=row-1, j=col-1; i>=0 && j>=0; i--, j--) {
+            if (chessboard[i][j] == 'Q') {
+                return false;
+            }
+        }
+
+        // 检查135度对角线
+        for (int i=row-1, j=col+1; i>=0 && j<=n-1; i--, j++) {
+            if (chessboard[i][j] == 'Q') {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+```
+