Problem p03874 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

typedef long long ll;
typedef pair<int, int> PP;

/*
    freopen("input","r",stdin);
    freopen("output","w",stdout);
*/

ll check(string s) {
  if (s.size() > 5000)
    return -1;
  ll DP[8];
  memset(DP, 0, sizeof(DP));
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'F')
      DP[0]++;
    if (s[i] == 'E')
      DP[1] += DP[0];
    if (s[i] == 'S')
      DP[2] += DP[1];
    if (s[i] == 'T')
      DP[3] += DP[2];
    if (s[i] == 'I')
      DP[4] += DP[3];
    if (s[i] == 'V')
      DP[5] += DP[4];
    if (s[i] == 'A')
      DP[6] += DP[5];
    if (s[i] == 'L')
      DP[7] += DP[6];
  }
  return DP[7];
}

int main() {
  ios::sync_with_stdio(false);
  ll K;
  cin >> K;
  ll DP[8];
  ll Q[8]; // Rem
  ll P[8]; // Number of Operation in second round.
  DP[7] = K;
  Q[0] = 1;
  for (int i = 7; i > 0; i--) {
    if (DP[i] <= 2) {
      DP[i - 1] = DP[i];
      Q[i] = DP[i];
    } else {
      ll T = min(400LL, DP[i] - 1);
      bool ok = 0;
      for (int j = T; j > 0 && ok == 0; j--) {
        if (DP[i] % j != 0) {
          Q[i] = DP[i] % j;
          DP[i - 1] = DP[i] / j;
          P[i] = j;
          ok = 1;
        }
      }
    }
  }
  string s = "FESTIVAL";
  string sol = s;
  for (int i = 7; i > 0; i--) {
    for (int j = Q[i]; j > 1; j--)
      sol.push_back(s[i]);
  }
  for (int i = 1; i < 8; i++) {
    for (int j = 0; j < P[i]; j++) {
      sol.push_back(s[i]);
    }
  }
  // ll ans = check(sol);
  // if (ans != K) cerr << "WRONG" << endl;
  cout << sol << endl;
  return 0;
}


Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

typedef long long ll;
typedef pair<int, int> PP;

/*
    freopen("input","r",stdin);
    freopen("output","w",stdout);
*/

ll check(string s) {
  if (s.size() > 5000)
    return -1;
  ll DP[8];
  memset(DP, 0, sizeof(DP));
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'F')
      DP[0]++;
    if (s[i] == 'E')
      DP[1] += DP[0];
    if (s[i] == 'S')
      DP[2] += DP[1];
    if (s[i] == 'T')
      DP[3] += DP[2];
    if (s[i] == 'I')
      DP[4] += DP[3];
    if (s[i] == 'V')
      DP[5] += DP[4];
    if (s[i] == 'A')
      DP[6] += DP[5];
    if (s[i] == 'L')
      DP[7] += DP[6];
  }
  return DP[7];
}

int main() {
  ios::sync_with_stdio(false);
  ll K;
  cin >> K;
  ll DP[8];
  ll Q[8]; // Rem
  ll P[8]; // Number of Operation in second round.
  memset(DP, 0, sizeof(DP));
  memset(Q, 0, sizeof(Q));
  memset(P, 0, sizeof(P));
  DP[7] = K;
  Q[0] = 1;
  for (int i = 7; i > 0; i--) {
    if (DP[i] <= 2) {
      DP[i - 1] = DP[i];
      Q[i] = DP[i];
    } else {
      ll T = min(400LL, DP[i] - 1);
      bool ok = 0;
      for (int j = T; j > 0 && ok == 0; j--) {
        if (DP[i] % j != 0) {
          Q[i] = DP[i] % j;
          DP[i - 1] = DP[i] / j;
          P[i] = j;
          ok = 1;
        }
      }
    }
  }
  string s = "FESTIVAL";
  string sol = s;
  for (int i = 7; i > 0; i--) {
    for (int j = Q[i]; j > 1; j--)
      sol.push_back(s[i]);
  }
  for (int i = 1; i < 8; i++) {
    for (int j = 0; j < P[i]; j++) {
      sol.push_back(s[i]);
    }
  }
  // ll ans = check(sol);
  // if (ans != K) cerr << "WRONG" << endl;
  cout << sol << endl;
  return 0;
}