题解 | #N皇后问题#

主要思路就是位运算，枚举每一行，然后当在某个(i,j)上放置之后将这一列和两个方向的对角线都标记上即可

class Solution {
public:
    /**
     * 
     * @param n int整型 the n
     * @return int整型
     */
    //diagonal1代表"/"，diagonal2代表“\”
    int dfs(int c, int diagonal1, int diagonal2, int r, int n){
        int ans = 0;
        if(r >= n){
            return 1;
        }
        //枚举第r行的第i列
        for(int i = 1; i <= n; ++i){
            if(!(c & (1<<(i-1))) && !(diagonal1 & (1<<(i+r))) && !(diagonal2 & (1<<(n-i+r+1)))){
                ans+=dfs(c | (1<<(i-1)), diagonal1 | (1<<(i+r)), diagonal2 | (1<<(n-i+r+1)), r+1, n);
            }
        }
        return ans;
    }
    int Nqueen(int n) {
        // write code here
        return dfs(0, 0, 0, 0, n);
    }
};