263 - Number Chains, uva

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#define db(a) \
cout << #a << " = " << a << endl
#define db2(a, b) \
cout << #a << " = " << a << " " << #b << " = " << b << endl
#define inf (1<<30)
#define foreach(m, it) \
for (typeof(m.begin()) it = m.begin(); it != m.end(); it++)
using namespace std;
int n;
bool espali(string linea) {
 int n = linea.size();
 for (int i = 0; i < n / 2; i++) {
  if (linea[i] != linea[n - i - 1])
   return false;
 }
 return true;
}
int main() {
 #ifdef dennisbot
  freopen("in.in", "r", stdin);
  freopen("ou.out", "w", stdout);
 #endif
 string s;
 char buf[10];
 int mayor, menor, prev, len;
 set<int> nums;
 while (cin >> s) {
  if (s == "0") break;
  prev = -1;
  len = 0;
  nums.clear();
  printf("Original number was %s\n", s.c_str());
  while (true) {
   sort(s.rbegin(), s.rend());
   mayor = atoi(s.c_str());
   reverse(s.begin(), s.end());
   menor = atoi(s.c_str());
   printf("%d - %d = %d\n", mayor, menor, mayor - menor);
   len++;
   prev = mayor - menor;
   if (!nums.count(prev))
    nums.insert(prev);
   else break;
   sprintf(buf, "%d", prev);
   s = buf;
  }
  printf("Chain length %d\n\n", len);
 }
 return 0;
}

Here is the Statement