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

#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>

using namespace std;

constexpr uint_fast64_t MOD = 1e9 + 7;

template <class StoreT, class AddT, class MulT, StoreT MOD> class ModInt {
  using self_type = ModInt<StoreT, AddT, MulT, MOD>;
  StoreT i;

public:
  ModInt() : i(0) {}
  ModInt(StoreT i) {
    while (i < 0)
      i += MOD;
    this->i = i;
  }

  ModInt(const self_type &i) = default;
  constexpr self_type &operator=(const self_type &i) = default;

  constexpr uint_fast32_t getI() const noexcept { return i; }

  ModInt &operator+=(self_type rhs) {
    AddT i64 = static_cast<AddT>(i);
    StoreT a32 = static_cast<StoreT>((i64 + rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator+(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt += rhs;
    return newInt;
  }

  ModInt &operator-=(self_type rhs) {
    AddT i64 = static_cast<AddT>(i);
    StoreT a32 = static_cast<StoreT>((i64 + MOD - rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator-(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt -= rhs;
    return newInt;
  }

  ModInt &operator*=(self_type rhs) {
    MulT i64 = static_cast<MulT>(i);
    StoreT a32 = static_cast<StoreT>((i64 * rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator*(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt *= rhs;
    return newInt;
  }

  constexpr ModInt operator/(self_type rhs) const noexcept {
    self_type newInt(*this);
    self_type rhsInv = rhs.inv();
    newInt *= rhsInv;
    return newInt;
  }

  constexpr bool operator==(self_type rhs) const noexcept { return i == rhs.i; }

  constexpr bool operator<(self_type rhs) const noexcept { return i < rhs.i; }

  constexpr bool operator>(self_type rhs) const noexcept { return rhs < *this; }

  constexpr ModInt pow(int n) const noexcept {
    ModInt a = *this;
    ModInt res = 1;

    while (n > 0) {
      if (n & 1) {
        res *= a;
      }
      a *= a;
      n >>= 1;
    }
    return res;
  }

  constexpr self_type inv() const noexcept { return pow(MOD - 2); }
};

template <class StoreT, class AddT, class MulT, StoreT MOD>
std::ostream &operator<<(std::ostream &ost, ModInt<StoreT, AddT, MulT, MOD> i) {
  ost << i.getI();
  return ost;
}

using UModInt = ModInt<uint_fast32_t, uint_fast32_t, uint_fast64_t, MOD>;
using SModInt = ModInt<int_fast32_t, int_fast32_t, int_fast64_t, MOD>;

template <class ModIntT> class BinomialFactory {
  std::vector<ModIntT> stock;
  std::vector<ModIntT> inv;

public:
  explicit BinomialFactory(int N) {
    stock.resize(N + 1);
    inv.resize(N + 1);
    stock[0] = 1;
    inv[0] = 1;
    for (int i = 1; i <= N; i++) {
      stock[i] = stock[i - 1] * i;
      inv[i] = stock[i].inv();
    }
  }

  ModIntT bi(int n, int r) const {
    if (r == 0 || r == n)
      return 1;

    return stock[n] * inv[n - r] * inv[r];
  }
};

int mm(int n) { return n * (n - 1) / 2; }

int main() {
  string S;
  cin >> S;

  constexpr int MM = 2019;
  using mint2019 = ModInt<uint_fast32_t, uint_fast32_t, uint_fast64_t, MM>;
  vector<int> bucket(MM, 0);

  mint2019 t = 0;
  for (int i = 0; i < S.size(); ++i) {
    int x = S.size() - i - 1;
    mint2019 d = S[x] - '0';
    d *= mint2019(10).pow(i);
    t += d;
    ++bucket[t.getI()];
  }

  int ans = mm(bucket[0] + 1);
  for (int i = 1; i < MM; ++i)
    ans += mm(bucket[i]);

  cout << ans << endl;
}


Error: TLE

Fixed submission:

#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>

using namespace std;

constexpr uint_fast64_t MOD = 1e9 + 7;

template <class StoreT, class AddT, class MulT, StoreT MOD> class ModInt {
  using self_type = ModInt<StoreT, AddT, MulT, MOD>;
  StoreT i;

public:
  ModInt() : i(0) {}
  ModInt(StoreT i) {
    while (i < 0)
      i += MOD;
    this->i = i;
  }

  ModInt(const self_type &i) = default;
  constexpr self_type &operator=(const self_type &i) = default;

  constexpr uint_fast32_t getI() const noexcept { return i; }

  ModInt &operator+=(self_type rhs) {
    AddT i64 = static_cast<AddT>(i);
    StoreT a32 = static_cast<StoreT>((i64 + rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator+(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt += rhs;
    return newInt;
  }

  ModInt &operator-=(self_type rhs) {
    AddT i64 = static_cast<AddT>(i);
    StoreT a32 = static_cast<StoreT>((i64 + MOD - rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator-(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt -= rhs;
    return newInt;
  }

  ModInt &operator*=(self_type rhs) {
    MulT i64 = static_cast<MulT>(i);
    StoreT a32 = static_cast<StoreT>((i64 * rhs.i) % MOD);
    i = a32;
    return *this;
  }

  constexpr ModInt operator*(self_type rhs) const noexcept {
    self_type newInt(*this);
    newInt *= rhs;
    return newInt;
  }

  constexpr ModInt operator/(self_type rhs) const noexcept {
    self_type newInt(*this);
    self_type rhsInv = rhs.inv();
    newInt *= rhsInv;
    return newInt;
  }

  constexpr bool operator==(self_type rhs) const noexcept { return i == rhs.i; }

  constexpr bool operator<(self_type rhs) const noexcept { return i < rhs.i; }

  constexpr bool operator>(self_type rhs) const noexcept { return rhs < *this; }

  constexpr ModInt pow(int n) const noexcept {
    ModInt a = *this;
    ModInt res = 1;

    while (n > 0) {
      if (n & 1) {
        res *= a;
      }
      a *= a;
      n >>= 1;
    }
    return res;
  }

  constexpr self_type inv() const noexcept { return pow(MOD - 2); }
};

template <class StoreT, class AddT, class MulT, StoreT MOD>
std::ostream &operator<<(std::ostream &ost, ModInt<StoreT, AddT, MulT, MOD> i) {
  ost << i.getI();
  return ost;
}

using UModInt = ModInt<uint_fast32_t, uint_fast32_t, uint_fast64_t, MOD>;
using SModInt = ModInt<int_fast32_t, int_fast32_t, int_fast64_t, MOD>;

template <class ModIntT> class BinomialFactory {
  std::vector<ModIntT> stock;
  std::vector<ModIntT> inv;

public:
  explicit BinomialFactory(int N) {
    stock.resize(N + 1);
    inv.resize(N + 1);
    stock[0] = 1;
    inv[0] = 1;
    for (int i = 1; i <= N; i++) {
      stock[i] = stock[i - 1] * i;
      inv[i] = stock[i].inv();
    }
  }

  ModIntT bi(int n, int r) const {
    if (r == 0 || r == n)
      return 1;

    return stock[n] * inv[n - r] * inv[r];
  }
};

int main() {
  string S;
  cin >> S;

  using mint2019 = ModInt<uint_fast32_t, uint_fast32_t, uint_fast64_t, 2019>;
  using vi = vector<int>;
  using vvi = vector<vector<int>>;

  vvi table(2019, vi(10));
  for (int i = 0; i < 2019; ++i)
    for (int j = 1; j <= 9; ++j)
      table[i][j] = (i * 10 + j) % 2019;

  int ans = 0;
  vector<int> dp;
  for (size_t i = 0; i < S.size(); i++) {
    int d = S[i] - '0';
    for (size_t j = 0; j < i; j++) {
      dp[j] = table[dp[j]][d];
      if (dp[j] == 0)
        ++ans;
      //            cout << dp[j] << " " << ans << endl;
    }
    dp.push_back(d);
  }

  cout << ans << endl;
}