Problem p02629 (C++) — buggy submission, verdict: Time Limit Exceeded

#include "bits/stdc++.h"
using namespace std;

using ll = long long int;
#define rep(i, a, b) for (int i = a; i < b; i++)
#define rrep(i, a, b) for (int i = a; i >= b; i--)
#define fore(i, a) for (auto &i : a)
#define all(x) (x).begin(), (x).end()

#define pi 3.14159265358979323846

template <class T> bool ch1000000(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

ll cnt_rep = 0;
ll powmod(ll N, ll P, ll M) {
  cnt_rep++;
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = powmod(N, P / 2, M);
    return t * t % M;
  }
  return (N * powmod(N, P - 1, M)) % M;
}

ll gcd(ll a, ll b) {
  ll resi, g, l;
  if (a > b) {
    g = a;
    l = b;
  } else if (b > a) {
    g = b;
    l = a;
  } else {
    return a;
  }
  resi = g % l;
  if (resi != 0) {
    return gcd(l, resi);
  } else {
    return l;
  }
}

template <typename T> void remove(std::vector<T> &vector, unsigned int index) {
  vector.erase(vector.begin() + index);
}

int ans = 0;
int N, M, Q;

template <typename T> void showall(vector<T> v) {
  rep(i, 0, v.size()) { cout << v[i] << " "; }
  cout << endl;
}

template <typename T> ll com(T n, T m, T mod) {
  ll a = 1, b = 1, ans;
  if (n == m || m == 0) {
    ans = 1;
  } else {
    for (ll i = 0; i < m; i++) {
      a *= n - i;
      a %= mod;
      b *= i + 1;
      b %= mod;
    }
    ans = (a * powmod(b, mod - 2, mod)) % mod;
  }

  return ans;
}

int main() {
  ll N;
  cin >> N;
  string ans = "";
  bool z = false;
  ll a = 1;

  while (true) {
    N--;
    ll resi = N % 26;
    char code = resi + 'a';
    ans += code;
    N /= 26;
    if (N <= 0)
      break;
  }

  reverse(all(ans));
  cout << ans << endl;

  // cout << setprecision(8) << ans << endl;  // For double
}


Error: TLE

Fixed submission:

#include "bits/stdc++.h"
using namespace std;

using ll = long long int;
#define rep(i, a, b) for (int i = a; i < b; i++)
#define rrep(i, a, b) for (int i = a; i >= b; i--)
#define fore(i, a) for (auto &i : a)
#define all(x) (x).begin(), (x).end()

#define pi 3.14159265358979323846

template <class T> bool ch1000000(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

ll cnt_rep = 0;
ll powmod(ll N, ll P, ll M) {
  cnt_rep++;
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = powmod(N, P / 2, M);
    return t * t % M;
  }
  return (N * powmod(N, P - 1, M)) % M;
}

ll gcd(ll a, ll b) {
  ll resi, g, l;
  if (a > b) {
    g = a;
    l = b;
  } else if (b > a) {
    g = b;
    l = a;
  } else {
    return a;
  }
  resi = g % l;
  if (resi != 0) {
    return gcd(l, resi);
  } else {
    return l;
  }
}

template <typename T> void remove(std::vector<T> &vector, unsigned int index) {
  vector.erase(vector.begin() + index);
}

int ans = 0;
int N, M, Q;

template <typename T> void showall(vector<T> v) {
  rep(i, 0, v.size()) { cout << v[i] << " "; }
  cout << endl;
}

template <typename T> ll com(T n, T m, T mod) {
  ll a = 1, b = 1, ans;
  if (n == m || m == 0) {
    ans = 1;
  } else {
    for (ll i = 0; i < m; i++) {
      a *= n - i;
      a %= mod;
      b *= i + 1;
      b %= mod;
    }
    ans = (a * powmod(b, mod - 2, mod)) % mod;
  }

  return ans;
}

int main() {
  ll N;
  cin >> N;
  string ans = "";
  bool z = false;

  while (true) {
    ll resi = N % 26;
    if (resi == 0) {
      resi = 26;
      z = true;
    }
    char code = resi + 96;
    ans += code;
    N /= 26;
    if (z)
      N -= 1;
    if (N == 0)
      break;
  }
  reverse(all(ans));
  cout << ans << endl;

  // cout << setprecision(8) << ans << endl;  // For double
}