原題

https://pintia.cn/problem-sets/994805260223102976/problems/994805302786899968

程式碼

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        int N1 = positiveOrder(num);
        int N2 = reverseOrder(num);
        int result=0;

        while ((result=(N2 - N1))!=6174){
            if (result==0) break;

            System.out.printf("%04d - %04d = %04d\n",N2,N1,result);

            N1 = positiveOrder(result);
            N2 = reverseOrder(result);
        }
        //輸出等於0或者6174的情況
        System.out.printf("%04d - %04d = %04d",N2,N1,result);
    }
    //遞增排序
    public static int positiveOrder ( int num){
            int[] arr = new int[4];
            for (int i = 0; i < 4; i++) {
                arr[i] = num % 10;
                num = num / 10;
            }
            Arrays.sort(arr);
            return arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];
        }
    //非遞增排序
    public static int reverseOrder ( int num){
            int[] arr = new int[4];
            for (int i = 0; i < 4; i++) {
                arr[i] = num % 10;
                num = num / 10;
            }
            Arrays.sort(arr);
            return arr[3] * 1000 + arr[2] * 100 + arr[1] * 10 + arr[0];
        }
}