排列式

import java.util.ArrayList;
import java.util.Collections;
public class j {
        //dzl
    static int[] a=new int[9];
    static ArrayList<String> l=new ArrayList<String>();
    public static void main(String[] args) {
        // TODO Auto-generated method stub
       f(0);
       Collections.sort(l);//排序
       //把集合遍历输出
       for (String c : l) {
        System.out.println(c);
    }
    }
    private static void f(int k) {
        //全排列1-9
        for (int i = 0; i <9; i++) {
            if(a[i]==0){
                a[i]=k+1;
                f(k+1);
                a[i]=0;
            }
        }
        //如果全排列完毕，算出是否满足乘法
        if(k==9){
            int sum1=a[0]*1000+a[1]*100+a[2]*10+a[3];
            int sum2=a[4]*10+a[5];
            int sum3=a[6]*100+a[7]*10+a[8];
            if(sum1==sum2*sum3){
                String b=sum1+" = "+sum2+" × "+sum3;
                l.add(b);
            }
            int sum4=a[4];
            int sum5=a[5]*1000+a[6]*100+a[7]*10+a[8];
            if(sum1==sum4*sum5){
                String b=sum1+" = "+sum4+" × "+sum5;
                l.add(b);
            }
        }
        
    }

}