题解：

1. 将输入的数字拆分装进数组 

2. 判断数组上的各位数字是否相等

3. 是 输出  n - n = 0000

4..否 将num循环重复 1 ；将数组排序，得到降序A,升序B；进而得到num;  直至 num == 6174

import java.io.*;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) throws IOException {
        // 使用io流包装
        StreamTokenizer in =new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));
        in.nextToken();
        int N=(int)in.nval,n=N;
        int[] arr=new int[4];
        int flag=1;
        for (int i = 0; i < 4; i++) {
            arr[i]=N%10;
            N/=10;
            if(i>0&&arr[i-1]!=arr[i])flag=0;
        }
        if (flag==1) System.out.printf("%04d - %04d = 0000\n",n,n);
        else {
                int A,B,num=n;
            while (true){
                for (int i = 0; i < 4; i++) {
                    arr[i]=num%10;
                    num/=10;
                }
                Arrays.sort(arr);
                A=0;B=0;
                for (int i = 0; i <4 ; i++) {
                    A=A*10+arr[3-i];
                    B=B*10+arr[i];
                }
                num=A-B;
                System.out.printf("%04d - %04d = %04d\n",A,B,num);
                if (num==6174)break;
            }
        }
    }
}