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

#include <bits/stdc++.h>
#ifdef LOCAL_DEBUG
#define DEBUG 1
#define CERR                                                                   \\
  if (DEBUG)                                                                   \\
  cerr
#define MACRO(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, NAME, ...) NAME
#define pr(...)                                                                \\
  CERR << MACRO(__VA_ARGS__, pr10, pr9, pr8, pr7, pr6, pr5, pr4, pr3, pr2,     \\
                pr1)(__VA_ARGS__)                                              \\
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define pr9(a, b, c, d, e, f, g, h, i) pr1(a) << pr8(b, c, d, e, f, g, h, i)
#define pr10(a, b, c, d, e, f, g, h, i, j)                                     \\
  pr1(a) << pr9(b, c, d, e, f, g, h, i, j)
#define prArr(a)                                                               \\
  {                                                                            \\
    CERR << (#a) << "={";                                                      \\
    int i = 0;                                                                 \\
    for (auto t : (a))                                                         \\
      CERR << (i++ ? ", " : "") << t;                                          \\
    CERR << "}" << endl;                                                       \\
  }
#else
#define DEBUG 0
#define pr(...)
#define prArr(a)
#endif
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL << 60) + 1e9; // ~ 1.15 * 1e18
const Int mod = (1e9) + 7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE

signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  string S;
  cin >> S;

  const Int mod = 2019;
  Int N = S.size();
  map<Int, Int> cnt;
  Int num = 0;
  vector<Int> A;
  Int t = 1;
  for (Int i = 0; i < N; i++) {
    num = num + (S[N - i - 1] - '0') * t;
    num %= mod;
    cnt[num]++;
    A.push_back(num);
    t = t * 10 % mod;
  }

  Int ans = 0;
  t = 1;
  Int ofset = 0;
  for (Int i = 0; i < N; i++) {
    ans += cnt[ofset];
    Int num = S[N - 1 - i] - '0';
    ofset += num * t % mod;
    ofset %= mod;
    t = t * 10 % mod;
    cnt[A[i]]--;
  }

  cout << ans << endl;

  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#ifdef LOCAL_DEBUG
#define DEBUG 1
#define CERR                                                                   \\
  if (DEBUG)                                                                   \\
  cerr
#define MACRO(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, NAME, ...) NAME
#define pr(...)                                                                \\
  CERR << MACRO(__VA_ARGS__, pr10, pr9, pr8, pr7, pr6, pr5, pr4, pr3, pr2,     \\
                pr1)(__VA_ARGS__)                                              \\
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define pr9(a, b, c, d, e, f, g, h, i) pr1(a) << pr8(b, c, d, e, f, g, h, i)
#define pr10(a, b, c, d, e, f, g, h, i, j)                                     \\
  pr1(a) << pr9(b, c, d, e, f, g, h, i, j)
#define prArr(a)                                                               \\
  {                                                                            \\
    CERR << (#a) << "={";                                                      \\
    int i = 0;                                                                 \\
    for (auto t : (a))                                                         \\
      CERR << (i++ ? ", " : "") << t;                                          \\
    CERR << "}" << endl;                                                       \\
  }
#else
#define DEBUG 0
#define pr(...)
#define prArr(a)
#endif
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL << 60) + 1e9; // ~ 1.15 * 1e18
const Int mod = 2019;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE

string S;
map<Int, Int> mem[200001];
_int used[200010][2019];

Int dfs(Int i, Int d) {
  if (i == (Int)S.size())
    return d == 0;
  if (used[i][d]++)
    return mem[i][d];
  Int num = S[i] - '0';
  Int res = dfs(i + 1, (d * 10 + num) % mod);
  res += d == 0;
  return mem[i][d] = res;
}

signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  cin >> S;

  Int ans = 0;
  Int N = S.size();
  for (Int i = 0; i < N; i++) {
    ans += dfs(i, 0) - 1;
  }
  cout << ans << endl;

  return 0;
}