Problem p02702 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
#define REP(i, b, e) for (int i = (b); i < (e); ++i)
#define RREP(i, b, e) for (int i = (b)-1; i >= e; --i)
#define rep(i, e) for (int i = 0; i < (e); ++i)

constexpr int MOD = 1000000007;
constexpr int INF = 1LL << 30;
constexpr long long LLINF = 1LL << 62;
constexpr double EPS = 1e-9;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15) << boolalpha;
  }
} initializer;

template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "[";
  for (auto it = vec.begin(); it != vec.end(); ++it) {
    if (it != vec.begin())
      os << ", ";
    os << *it;
  }
  return os << "]";
}

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &pa) {
  return os << "(" << pa.first << ", " << pa.second << ")";
}

template <typename Tuple, size_t N> struct TuplePrinter {
  static void print(const Tuple &t) {
    TuplePrinter<Tuple, N - 1>::print(t);
    cout << ", " << get<N - 1>(t);
  }
};

template <typename Tuple> struct TuplePrinter<Tuple, 1> {
  static void print(const Tuple &t) { cout << get<0>(t); }
};

template <typename... T>
ostream &operator<<(ostream &os, const tuple<T...> &tup) {
  os << "(";
  TuplePrinter<decltype(tup), sizeof...(T)>::print(tup);
  return os << ")";
}

template <typename T> ostream &operator<<(ostream &os, const set<T> &se) {
  os << "{";
  for (auto it = se.begin(); it != se.end(); ++it) {
    if (it != se.begin())
      os << ", ";
    os << *it;
  }
  return os << "}";
}

template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &ma) {
  os << "{";
  for (auto it = ma.begin(); it != ma.end(); ++it) {
    if (it != ma.begin())
      os << ", ";
    os << it->first << ": " << it->second;
  }
  return os << "}";
}

inline void print(void) { cout << '\\n'; }
template <class T> inline void print(const T &x) { cout << x << '\\n'; }
template <class T, class... U> inline void print(const T &x, const U &...y) {
  cout << x << " ";
  print(y...);
}
#define dump(...)                                                              \\
  cout << #__VA_ARGS__ << ": [L_" << __LINE__ << "]" << '\\n';                  \\
  print(__VA_ARGS__);                                                          \\
  cout << '\\n';

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

int main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<long long> dp(2020, 0);
  vector<long long> tmp1(2020, 0);
  vector<long long> tmp2(2020, 0);
  int rem = (s[0] - '0') % 2019;
  dp[rem] = 1;
  tmp1[rem] = 1;

  REP(i, 1, n) {
    ++tmp2[(s[i] - '0')];
    rep(j, 2020) if (tmp1[j] != 0) {
      int rem = (j * 10 + (s[i] - '0')) % 2019;
      tmp2[rem] += tmp1[j];
    }
    rep(j, 2020) if (tmp2[j] != 0) { dp[j] += tmp2[j]; }
    swap(tmp1, tmp2);
    fill(tmp2.begin(), tmp2.end(), 0);
  }

  print(dp[0]);

  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define REP(i, b, e) for (int i = (b); i < (e); ++i)
#define RREP(i, b, e) for (int i = (b)-1; i >= e; --i)
#define rep(i, e) for (int i = 0; i < (e); ++i)

constexpr int MOD = 1000000007;
constexpr int INF = 1LL << 30;
constexpr long long LLINF = 1LL << 62;
constexpr double EPS = 1e-9;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15) << boolalpha;
  }
} initializer;

template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "[";
  for (auto it = vec.begin(); it != vec.end(); ++it) {
    if (it != vec.begin())
      os << ", ";
    os << *it;
  }
  return os << "]";
}

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &pa) {
  return os << "(" << pa.first << ", " << pa.second << ")";
}

template <typename Tuple, size_t N> struct TuplePrinter {
  static void print(const Tuple &t) {
    TuplePrinter<Tuple, N - 1>::print(t);
    cout << ", " << get<N - 1>(t);
  }
};

template <typename Tuple> struct TuplePrinter<Tuple, 1> {
  static void print(const Tuple &t) { cout << get<0>(t); }
};

template <typename... T>
ostream &operator<<(ostream &os, const tuple<T...> &tup) {
  os << "(";
  TuplePrinter<decltype(tup), sizeof...(T)>::print(tup);
  return os << ")";
}

template <typename T> ostream &operator<<(ostream &os, const set<T> &se) {
  os << "{";
  for (auto it = se.begin(); it != se.end(); ++it) {
    if (it != se.begin())
      os << ", ";
    os << *it;
  }
  return os << "}";
}

template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &ma) {
  os << "{";
  for (auto it = ma.begin(); it != ma.end(); ++it) {
    if (it != ma.begin())
      os << ", ";
    os << it->first << ": " << it->second;
  }
  return os << "}";
}

inline void print(void) { cout << '\\n'; }
template <class T> inline void print(const T &x) { cout << x << '\\n'; }
template <class T, class... U> inline void print(const T &x, const U &...y) {
  cout << x << " ";
  print(y...);
}
#define dump(...)                                                              \\
  cout << #__VA_ARGS__ << ": [L_" << __LINE__ << "]" << '\\n';                  \\
  print(__VA_ARGS__);                                                          \\
  cout << '\\n';

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

int main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<vector<int>> dp(200010, vector<int>(2020, 0));
  int rem = (s[0] - '0') % 2019;
  dp[0][rem] = 1;

  vector<int> tmp(2020, 0);

  REP(i, 1, n) {
    fill(tmp.begin(), tmp.end(), 0);
    ++tmp[(s[i] - '0')];
    rep(j, 2020) if (dp[i - 1][j] > 0) {
      int rem = (j * 10 + (s[i] - '0')) % 2019;
      tmp[rem] += 1;
    }
    rep(j, 2020) if (tmp[j] > 0) { dp[i][j] += tmp[j]; }
  }
  long long ans = 0;
  rep(i, n) ans += dp[i][0];
  print(ans);

  return 0;
}