n皇后问题

import java.util.*;

public class Queens {
    int total=0;
    public int nQueens(int n) {
        int[][] vis=new int[3][n<<1];
        search(0,vis,n);
        return total;
    }
    private void search(int cur, int[][] vis,int n) {
        if(cur==n){
            total++;
            return;
        }
        for(int i=0;i<n;i++){
            if(vis[0][i]==0&&vis[1][cur+i]==0&&vis[2][cur-i+n]==0){
                vis[0][i]=vis[1][cur+i]=vis[2][cur-i+n]=1;
                search(cur+1,vis,n);
                vis[0][i]=vis[1][cur+i]=vis[2][cur-i+n]=0;
            }
        }
    }
}