Problem p00254 (C++)

Buggy submission (status: Time Limit Exceeded):
#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;

// #define int long long
#define DBG 1
#define dump(o)                                                                \
  if (DBG) {                                                                   \
    cerr << #o << " " << o << endl;                                            \
  }
#define dumpc(o)                                                               \
  if (DBG) {                                                                   \
    cerr << #o;                                                                \
    for (auto &e : (o))                                                        \
      cerr << " " << e;                                                        \
    cerr << endl;                                                              \
  }
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define each(it, c) for (auto it = (c).begin(); it != (c).end(); it++)
#define all(c) c.begin(), c.end()
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9 + 7);
bool NA(string s) {
  if (s == "1111" || s == "2222" || s == "3333" || s == "4444" || s == "5555" ||
      s == "6666" || s == "7777" || s == "8888" || s == "9999")
    return true;
  else
    return false;
}
signed main() {
  string s;
  while (cin >> s, s != "0000") {
    int ans(0);
    while (s != "6174") {
      if (NA(s)) {
        cout << "NA" << endl;
        goto here;
      }
      string big(s), small(s);
      sort(all(small));
      sort(all(big), greater<char>());
      s = to_string(stoi(big) - stoi(small));
      ans++;
    }
    cout << ans << endl;
  here:;
  }
  return 0;
}

Fixed submission:
#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;

// #define int long long
#define DBG 1
#define dump(o)                                                                \
  if (DBG) {                                                                   \
    cerr << #o << " " << o << endl;                                            \
  }
#define dumpc(o)                                                               \
  if (DBG) {                                                                   \
    cerr << #o;                                                                \
    for (auto &e : (o))                                                        \
      cerr << " " << e;                                                        \
    cerr << endl;                                                              \
  }
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define each(it, c) for (auto it = (c).begin(); it != (c).end(); it++)
#define all(c) c.begin(), c.end()
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9 + 7);
bool NA(string s) {
  if (s == "1111" || s == "2222" || s == "3333" || s == "4444" || s == "5555" ||
      s == "6666" || s == "7777" || s == "8888" || s == "9999")
    return true;
  else
    return false;
}
signed main() {
  string s;
  while (cin >> s, s != "0000") {
    int ans(0);
    while (s != "6174") {
      if (NA(s)) {
        cout << "NA" << endl;
        goto here;
      }
      string big(s), small(s);
      sort(all(small));
      sort(all(big), greater<char>());
      s = to_string(stoi(big) - stoi(small));
      while (s.size() < 4)
        s = "0" + s;
      ans++;
    }
    cout << ans << endl;
  here:;
  }
  return 0;
}