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

#include "bits/stdc++.h"

using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;
typedef long long LL;
typedef priority_queue<int> PQ_DESC;
typedef priority_queue<int, vector<int>, greater<int>> PQ_ASC;
typedef priority_queue<PII> PQ_DESC_PII;
typedef priority_queue<PII, vector<PII>, greater<PII>> PQ_ASC_PII;

#define ALL(c) (c).begin(), (c).end()
#define PB push_back
#define MP make_pair
#define SORT_ASC(c) sort(ALL(c))
#define SORT_DESC(c) sort(ALL(c), greater<typeof(*((c).begin()))>())
#define SIZE(a) int((a).size())

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define ROF(i, a, b) for (int i = (b - 1); i >= (a); --i)
#define REP(i, n) FOR(i, 0, n)
#define PER(i, n) ROF(i, 0, n)

const double EPS = 1e-10;
const double PI = acos(-1.0);
const int LARGE_INT = 1e9 + 100;
const int INF = 2e9 + 100;
const LL INF_LL = (LL)INF * 300 * 300;
const int MOD = 2019;

// debug
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

LL modpow(LL a, LL n) {
  LL res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % MOD;
    a = a * a % MOD;
    n >>= 1;
  }
  return res;
}

void Main() {
  string s;
  cin >> s;
  int n = SIZE(s);
  reverse(ALL(s));

  REP(i, n) { s[i] -= '0'; }

  vector<LL> a(n);
  a[0] = s[0];
  FOR(i, 1, n) {
    a[i] = (a[i - 1] + modpow(10, i) * s[i]) % MOD;
    // dump(s[i]+'0')
  }

  VI c(MOD + 1);
  c[0]++;
  REP(i, n) {
    c[a[i]]++;
    // dump(a[i])
  }

  LL result = 0;

  REP(i, MOD + 1) { result += c[i] * (c[i] - 1) / 2; }

  cout << result << endl;

  return;
}

int main() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  Main();
  return 0;
}

Error: TLE

Fixed submission:

#include "bits/stdc++.h"

using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;
typedef long long LL;
typedef priority_queue<int> PQ_DESC;
typedef priority_queue<int, vector<int>, greater<int>> PQ_ASC;
typedef priority_queue<PII> PQ_DESC_PII;
typedef priority_queue<PII, vector<PII>, greater<PII>> PQ_ASC_PII;

#define ALL(c) (c).begin(), (c).end()
#define PB push_back
#define MP make_pair
#define SORT_ASC(c) sort(ALL(c))
#define SORT_DESC(c) sort(ALL(c), greater<typeof(*((c).begin()))>())
#define SIZE(a) int((a).size())

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define ROF(i, a, b) for (int i = (b - 1); i >= (a); --i)
#define REP(i, n) FOR(i, 0, n)
#define PER(i, n) ROF(i, 0, n)

const double EPS = 1e-10;
const double PI = acos(-1.0);
const int LARGE_INT = 1e9 + 100;
const int INF = 2e9 + 100;
const LL INF_LL = (LL)INF * 300 * 300;
const int MOD = 1e9 + 7;

// debug
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

LL modpow(LL a, LL n) {
  LL res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % MOD;
    a = a * a % MOD;
    n >>= 1;
  }
  return res;
}

void Main() {
  string s;
  cin >> s;
  int n = SIZE(s);

  LL result = 0;

  REP(i, n) {
    int t = 0;
    FOR(j, i, n) {
      t += s[j] - '0';
      if (t % 2019 == 0) {
        result++;
      }
      t %= 2019;
      t *= 10;
    }
  }

  cout << result << endl;

  return;
}

int main() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  Main();
  return 0;
}