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

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

#define rep(i, n, m) for (int i = (n); i < (m); i++)
#define rep_d(i, n, m) for (int i = (n)-1; i >= (m); i--)
#define sort_asc(X) sort((X).begin(), (X).end())
#define sort_desc(X) sort((X).begin(), (X).end(), greater<>())
#define endl "\\n"

template <class T> bool chmax(T &a, T b);
template <class T> bool chmin(T &a, T b);
int *eratosthenes(int N);
bool bit_search(int pattern, int N);
void initialize(void);

const ll INF = 1LL << 60;
const int k_mod = 1e9 + 7;
template <typename T, typename K> struct P {
  T a;
  K b;
};
typedef struct {
  vector<int> to;
  int cost;
} edge;

int main(void) {
  // initialize();
  string S;
  cin >> S;
  int N = S.size();
  int prev[2019] = {};
  ll ans = 0;

  prev[(int)(S[0] - '0')] = 1;
  rep(i, 1, N) {
    int num = (int)(S[i] - '0');
    int now[2019] = {};
    rep(j, 0, 2019) {
      if (prev[j] != 0) {
        int temp = prev[j];
        now[(j * 10 + num) % 2019] = temp;
      }
    }
    now[num]++;
    ans += now[0];
    rep(i, 0, 2019) { prev[i] = now[i]; }
  }
  cout << ans << endl;
}

template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
int *eratosthenes(int N) {
  int *prime_array = new int[N + 1];
  int lim = N;
  prime_array[0] = 0;
  prime_array[1] = 0;
  rep(i, 2, N + 1) { prime_array[i] = 1; }
  rep(i, 2, lim) {
    if (prime_array[i] == 0)
      continue;
    lim = N / i;
    for (int j = i * 2; j < N + 1; j += i) {
      prime_array[j] = 0;
    }
  }
  return prime_array;
}
bool bit_search(int pattern, int N) {
  int cnt = 0;
  rep(bit, 0, N) {
    if (pattern & (1 << bit)) {
      cnt++;
    }
  }
  return true;
}
void initialize(void) { cout << fixed << setprecision(10); }


Error: MLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

#define rep(i, n, m) for (int i = (n); i < (m); i++)
#define rep_d(i, n, m) for (int i = (n)-1; i >= (m); i--)
#define sort_asc(X) sort((X).begin(), (X).end())
#define sort_desc(X) sort((X).begin(), (X).end(), greater<>())
#define endl "\\n"

template <class T> bool chmax(T &a, T b);
template <class T> bool chmin(T &a, T b);
int *eratosthenes(int N);
bool bit_search(int pattern, int N);
void initialize(void);

const ll INF = 1LL << 60;
const int k_mod = 1e9 + 7;
template <typename T, typename K> struct P {
  T a;
  K b;
};
typedef struct {
  vector<int> to;
  int cost;
} edge;

int main(void) {
  // initialize();
  string S;
  cin >> S;
  int N = S.size();
  vector<int *> vec(N);
  rep(i, 0, N) { vec[i] = new int[2019]{}; }
  ll ans = 0;
  vec[0][(int)(S[0] - '0')] = 1;
  rep(i, 1, N) {
    int num = (int)(S[i] - '0');
    rep(j, 0, 2019) {
      if (vec[i - 1][j] != 0) {
        int temp = vec[i - 1][j];
        vec[i][(j * 10 + num) % 2019] = temp;
      }
    }
    vec[i][num]++;
    ans += vec[i][0];
  }
  cout << ans << endl;
}

template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
int *eratosthenes(int N) {
  int *prime_array = new int[N + 1];
  int lim = N;
  prime_array[0] = 0;
  prime_array[1] = 0;
  rep(i, 2, N + 1) { prime_array[i] = 1; }
  rep(i, 2, lim) {
    if (prime_array[i] == 0)
      continue;
    lim = N / i;
    for (int j = i * 2; j < N + 1; j += i) {
      prime_array[j] = 0;
    }
  }
  return prime_array;
}
bool bit_search(int pattern, int N) {
  int cnt = 0;
  rep(bit, 0, N) {
    if (pattern & (1 << bit)) {
      cnt++;
    }
  }
  return true;
}
void initialize(void) { cout << fixed << setprecision(10); }