pat1019：数字黑洞

https://www.patest.cn/contests/pat-b-practise/1019

#include "stdio.h"

void swap(int *c, int *d)
{
int temp;
temp = *c;
*c = *d;
*d = temp;
}
void kap(int k)
{
int i, j, max, min;
int a[4] = {k/1000, (k%1000)/100, (k%100)/10, k%10};
if((a[0] == a[1]) && (a[1] == a[2]) && (a[2] == a[3]))
{
printf("%d - %d = 0000\n", k, k);
return ;
}
for(i = 0; i < 4; ++i)
for(j = i+1; j < 4; ++j)
if(a[i] < a[j])
swap(&a[i], &a[j]);
max = a[0] * 1000 + a[1] * 100 + a[2] * 10 + a[3];
min = a[3] * 1000 + a[2] * 100 + a[1] * 10 + a[0];
printf("%04d - %04d = %04d\n", max, min, max - min);
if(6174 != max - min)
kap(max - min);
}
int main()
{
int k;
scanf("%d", &k);
kap(k);

return 0;
}