2. /**
    3.  * @param {number} n
    4.  * @return {string[][]}
    5.  */
    6. let result = [];
    7. var solveNQueens = function(n) {
    8.     result = [];
    9.     let board = [];
    10.     for (let i = 0; i < n; i++) {
    11.       board[i] = [];
    12.       for (let j = 0; j < n; j++) {
    13.         board[i][j] = '.'
    14.       }
    15.     }
    16.     backtrack(0, board, n);
    17.     return result;
    18. };
    19. function deepClone(board) {
    20.   let res = [];
    21.   for (let i = 0; i < board.length; i++) {
    22.     res.push(board[i].join(''));
    23.   }
    24.   return res;
    25. }
    26. function backtrack(row, board, n) {
    27.     if (row === n) {
    28.       result.push(deepClone(board));
    29.       return;
    30.     }
    31.     for (let j = 0; j < n; j++) {
    32.         if (checkInValid(board, row, j, n)) continue;
    33.         board[row][j] = 'Q';
    34.         backtrack(row + 1, board, n);
    35.         board[row][j] = '.';
    36.       }
    37. }
    38. function checkInValid(board, row, column, n) {
    39.   // 行
    40.   for (let i = 0; i < n; i++) {
    41.     if (board[i][column] === 'Q') return true;
    42.   }
    43.   for (let i = row - 1, j = column + 1; i >= 0 && j < n; i--, j++) {
    44.     if (board[i][j] === 'Q') return true;
    45.   }
    46.   for (let i = row - 1, j = column - 1; i >= 0 && j >= 0; i--, j--) {
    47.     if (board[i][j] === 'Q') return true;
    48.   }
    49.   return false;
    50. }