52. N皇后 II

题意：

解题思路：

思路：
1. 解法同：51. N皇后

PHP代码实现：

class Solution {
  public $cols = [];
  public $pie = [];
  public $na = [];
  public $res = [];
  function totalNQueens($n) {
    $this->solve([], $n, 0);
    return count($this->res);
  }
  function solve($answer, $n, $i) {
    if ($i == $n) {
      array_push($this->res, $answer);
      return;
    }
    for ($j = 0; $j < $n; $j++) {
      if (in_array($j, $this->cols) || in_array($i + $j, $this->pie) || in_array($i - $j + $n, $this->na)) {
        continue;
      }
      array_push($this->cols, $j);
      array_push($this->pie, $i + $j);
      array_push($this->na, $i - $j + $n);
      $answer[$i] = $j;
      $this->solve($answer, $n, $i + 1);
      array_pop($this->cols);
      array_pop($this->pie);
      array_pop($this->na);
    }
  }
}

GO代码实现：

func totalNQueens(n int) int {
    res := make([][]int, 0)
    cols := make(map[int]bool, n)
    pie := make(map[int]bool, n)
    na := make(map[int]bool, n)
    dfs([]int{}, n, cols, pie, na, &res)
    return len(res)
}
func dfs(rows []int, n int, cols, pie, na map[int]bool, res *[][]int) {
    row := len(rows)
    if row == n {
        temp := make([]int, len(rows))
        copy(temp, rows)
        (*res) = append((*res), temp)
        return
    }
    for col := 0; col < n; col++ {
        if !cols[col] && !pie[row + col] && !na[row - col] {
            cols[col], pie[row + col], na[row - col]  = true, true, true;
            dfs(append(rows, col), n, cols, pie, na, res)
            cols[col], pie[row + col], na[row - col]  = false, false, false;
        }
    }
}