Merge pull request youngyangyang04#1201 from xiaofei-2020/back20

添加（0051.N皇后.md）：增加typescript版本

Author: youngyangyang04

problems/0051.N皇后.md

@@ -457,6 +457,58 @@ var solveNQueens = function(n) {
 };
 ```
 
+## TypeScript
+
+```typescript
+function solveNQueens(n: number): string[][] {
+    const board: string[][] = new Array(n).fill(0).map(_ => new Array(n).fill('.'));
+    const resArr: string[][] = [];
+    backTracking(n, 0, board);
+    return resArr;
+    function backTracking(n: number, rowNum: number, board: string[][]): void {
+        if (rowNum === n) {
+            resArr.push(transformBoard(board));
+            return;
+        }
+        for (let i = 0; i < n; i++) {
+            if (isValid(i, rowNum, board) === true) {
+                board[rowNum][i] = 'Q';
+                backTracking(n, rowNum + 1, board);
+                board[rowNum][i] = '.';
+            }
+        }
+    }
+};
+function isValid(col: number, row: number, board: string[][]): boolean {
+    const n: number = board.length;
+    if (col < 0 || col >= n || row < 0 || row >= n) return false;
+    // 检查列
+    for (let row of board) {
+        if (row[col] === 'Q') return false;
+    }
+    // 检查45度方向
+    let x: number = col,
+        y: number = row;
+    while (y >= 0 && x < n) {
+        if (board[y--][x++] === 'Q') return false;
+    }
+    // 检查135度方向
+    x = col;
+    y = row;
+    while (x >= 0 && y >= 0) {
+        if (board[y--][x--] === 'Q') return false;
+    }
+    return true;
+}
+function transformBoard(board: string[][]): string[] {
+    const resArr = [];
+    for (let row of board) {
+        resArr.push(row.join(''));
+    }
+    return resArr;
+}
+```
+
 ### Swift
 
 ```swift