试题名称 算法提高 数字黑洞——Java（递归）

import java.util.*;

public class Main {

    public static void main(String[] args) {
			Scanner sc = new Scanner(System.in);
			int r = sc.nextInt();
        int f = f(r);
        System.out.println(f);
    }
    public static int f(int n) {
        if (n == 6174) {
            return 0;
        }
        return f(res(n))+1;
    }
    public static int res(int n){
        int nums[] = new int[4];
        int cnt = 0;
        while (n != 0){
            int x = n%10;
            nums[cnt++] = x;
            n /= 10;
        }
        Arrays.sort(nums);
        return ((nums[3]*1000+nums[2]*100+nums[1]*10+nums[0])-(nums[0]*1000+nums[1]*100+nums[2]*10+nums[3]));
    }
}