[51] N 皇后

/**
 * @param {number} n
 * @return {string[][]}
 */
const solveNQueens = function (n) {
  const ans = [];
  const initialMap = Array.from(Array(n), item => new Array(n).fill('.'));
  const canUse = function (zmap, row, col) {
    for (let i = 0; i < row; i++) {
      if (zmap[i][col] === 'Q') {
        return false;
      }
      if (col - row + i >= 0 && zmap[i][col - row + i] === 'Q') {
        return false;
      }
      if (col + row - i < n && zmap[i][col + row - i] === 'Q') {
        return false;
      }
    }
    return true;
  };
  const dps = function (zmap, row) {
    if (row === n) {
      ans.push(zmap.map(item => item.join('')));
    } else {
      for (let k = 0; k < n; k++) {
        if (canUse(zmap, row, k)) {
          const newMap = JSON.parse(JSON.stringify(zmap));
          newMap[row][k] = 'Q';
          dps(newMap, row + 1);
        }
      }
    }
  };
  dps(initialMap, 0);
  return ans;
};