Search special --DFS

Eight queens problem

https://www.luogu.org/recordnew/show/19470456

1. This problem was first thought was explosive search each node possible, using the back were looking ,, but this time complexity is $O (2 ^ n)$certainly Index explosion
2. We traversed once for each layer can
   precisely place each per row and a queen, if C [x] represents a column number row x Queen, the problem becomes full permutation generation problem. And n is 0 to arranged a total of only n!, At least smaller than the index.

import java.util.Scanner;

public class Main{

    private int[] col = new int[20];
    private boolean[][] use = new boolean[3][100];
    private int size;
    private int[] result = new int[20];
    private int ans = 0;

    public void get_data(){
        Scanner in = new Scanner(System.in);
        size= in.nextInt();
    }

    public void dfs(int i){
        if(i==size+1) {
            ans++;
            if(ans<=3)
                this.output();
            return;
        }

        for(int j=1;j<=size;j++){
            if(!use[0][j]&&!use[1][i+j]&&!use[2][i-j+size]) {
                result[i] = j;
                use[0][j] = use[1][i+j] = use[2][i-j+size] = true;
                dfs(i+1);
                use[0][j] = use[1][i+j] = use[2][i-j+size] = false;
            }
        }
    }

    public void solve(){
        dfs(1);
        System.out.println(ans);
    }

    public void output(){
        for(int i=1;i<=size;i++){
            System.out.print(result[i]+" ");
        }
        System.out.println();
    }


    public static void main(String arg[]){
        Main obj = new Main();
        obj.get_data();
        obj.solve();
    }
}