六角填数（DFS）

import java.util.*;

public class Main {

    public static void main(String[] args) {
        int[] b = new int[7];
        int[] a = new int[13];
        int[] flag = new int[13];
        a[1] = 1;
        a[2] = 8;
        a[12] = 3;
        flag[1] = 1;
        flag[8] = 1;
        flag[3] = 1;
        int res = dfs(a,b,flag,3);
        for(int i = 1;i <= 12;i++){
            System.out.print(a[i] +" ");
        }
        System.out.println();
        System.out.println("*位的数字是:" + res);
    }
    public static int judge(int[] a ,int[] b){
        b[1] = a[1] + a[3] + a[6] + a[8];
        b[2] = a[1] + a[4] + a[7] + a[11];
        b[3] = a[8] + a[9] + a[10] + a[11];
        b[4] = a[2] + a[6] + a[9] + a[12];
        b[5] = a[5] + a[7] + a[10] + a[12];
        b[6] = a[2] + a[3] + a[4] + a[5];

        for(int i = 2;i <= 6;i++){
            if(b[i]!=b[i-1])
                return -1;
        }
        return a[6];
    }
    public static int dfs(int[] a,int[] b,int[] flag,int str){

        for(int i = 1;i <= 12;i++){
            if(flag[i] == 0){
                //说明这个数字可以使用
                a[str] = i;
                flag[i] = i;
                if(str == 11){
                    int res = judge(a,b);
                    if(res == -1){
                        flag[i] = 0;
                        break;
                    }
                    else{
                        return res;
                    }
                }
                int res =  dfs(a,b,flag,str+1);
                if(res == -1){
                    flag[i] = 0;
                }
                else{
                    return res;
                }
            }
        }
        return -1;
    }
}