牛客网：NC39 N皇后问题

import java.util.*;


public class Solution {
    /**
     * 
     * @param n int整型 the n
     * @return int整型
     */
    int res = 0;
    public int Nqueen (int n) {
        // write code here
        int[] pd = new int[n];
        recursion(n, 0, pd);
        return res;
    }
    
    private void recursion(int n, int row, int[] pow){
        if (n == row){
            res++;
            return;
        }
        
        for (int i = 0; i < n; i++){
            if (isVaild(row, i, pow)){
                pow[row] = i;
                recursion(n, row + 1, pow);
            }
        }
        
    }
    
    private boolean isVaild (int row, int col, int[] pow){
        for (int i = 0; i < row; i++){
            if (i == row || pow[i] == col || Math.abs(row - i) == Math.abs(pow[i] - col)){
                return false;
            }
        }
        return true;
    }
}