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

#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

/* template */

using ll = long long;

void debug_out() { std::cout << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...)                                                             \\
  cout << "debug: ";                                                           \\
  debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

#define rep(i, a, n) for (int i = (int)(a); i < (int)(n); i++)
#define rrep(i, a, n) for (int i = ((int)(n - 1)); i >= (int)(a); i--)
#define Rep(i, a, n) for (long long i = (long long)(a); i < (long long)(n); i++)
#define RRep(i, a, n)                                                          \\
  for (long long i = ((long long)(n - 1ll)); i >= (long long)(a); i--)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

struct Edge {
  int to;
  ll weight;
  Edge(int t, ll w) : to(t), weight(w) {}
};

struct edge {
  int from;
  int to;
  ll weight;
  edge(int f, int t, ll w) : from(f), to(t), weight(w) {}
};

using Graph = vector<vector<Edge>>;
using graph = vector<vector<int>>;
using edges = vector<edge>;

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> T lcm(T a, T b) { return (a * b) / gcd(a, b); }

bool isPalindrome(string s) {
  string t = s;
  reverse(all(t));
  return s == t;
}

constexpr ll LNF = __LONG_LONG_MAX__;

constexpr int INF = 1e9 + 7;

const double PI = 3.14159265358979323846;

vector<int> dx = {-1, 0, 1, 0, -1, 1, -1, 1};
vector<int> dy = {0, -1, 0, 1, 1, -1, -1, 1};

/* template */

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  int n = s.size();
  vector<int> dp(n + 1, 0);
  int p = 1;
  reverse(all(s));
  vector<ll> m(2019, 0);
  rep(i, 0, n) {
    dp[i + 1] = (dp[i] + (s[i] - '0') * p) % 2019;
    p *= 10;
    p %= 2019;
    m[dp[i]]++;
  }
  m[dp[n]]++;
  ll ans = 0;
  rep(i, 0, 2019) { ans += (m[i] - 1) * m[i] / 2; }
  cout << ans << endl;
}

Error: TLE

Fixed submission:

#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

/* template */

using ll = long long;

void debug_out() { std::cout << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...)                                                             \\
  cout << "debug: ";                                                           \\
  debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

#define rep(i, a, n) for (int i = (int)(a); i < (int)(n); i++)
#define rrep(i, a, n) for (int i = ((int)(n - 1)); i >= (int)(a); i--)
#define Rep(i, a, n) for (long long i = (long long)(a); i < (long long)(n); i++)
#define RRep(i, a, n)                                                          \\
  for (long long i = ((long long)(n - 1ll)); i >= (long long)(a); i--)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

struct Edge {
  int to;
  ll weight;
  Edge(int t, ll w) : to(t), weight(w) {}
};

struct edge {
  int from;
  int to;
  ll weight;
  edge(int f, int t, ll w) : from(f), to(t), weight(w) {}
};

using Graph = vector<vector<Edge>>;
using graph = vector<vector<int>>;
using edges = vector<edge>;

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <class T> T lcm(T a, T b) { return (a * b) / gcd(a, b); }

bool isPalindrome(string s) {
  string t = s;
  reverse(all(t));
  return s == t;
}

constexpr ll LNF = __LONG_LONG_MAX__;

constexpr int INF = 1e9 + 7;

const double PI = 3.14159265358979323846;

vector<int> dx = {-1, 0, 1, 0, -1, 1, -1, 1};
vector<int> dy = {0, -1, 0, 1, 1, -1, -1, 1};

/* template */

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  vector<vector<pair<int, int>>> dp(s.size());
  dp[0].emplace_back(s[0] - '0', 1);
  ll ans = 0;
  rep(i, 1, s.size()) {
    int flag = 0;
    rep(j, 0, dp[i - 1].size()) {
      pair<int, int> x = dp[i - 1][j];
      int l = x.first * 10 + (s[i] - '0');
      l %= 2019;
      if (l == 0) {
        ans += x.second;
      }
      if (l == (s[i] - '0')) {
        flag = 1;
        x.second++;
      }
      dp[i].emplace_back(l, x.second);
    }
    if (flag == 0) {
      dp[i].emplace_back((s[i] - '0'), 1);
    }
  }
  cout << ans << endl;
}