避免数位排序的方法：桶排。

#include <cstdio>
#include <cstring>

int digit[10];

int process(int m){
    memset(digit, 0, sizeof(digit));
    ++ digit[m / 1000];
    ++ digit[(m % 1000) / 100];
    ++ digit[(m % 100) / 10];
    ++ digit[m % 10];
    int big = 0, small = 0, timer = 1;
    for(int i = 0; i <= 9; ++ i){
        while(digit[i]){
            big += i * timer;
            small += i * 1000 / timer;
            timer *= 10;
            -- digit[i];
        }
    }
    return big - small;
}

int main(){
    int n, i;
    int num, cnt = 0;
    scanf("%d", &n);
    for(i = 1; i <= n; ++ i){
        scanf("%d", &num);
        while(num != 6174){
            num = process(num);
            ++ cnt;
        }
        printf("%d\n", cnt + 1);
        cnt = 0;
    }
}