Problem p02702 (C++)

Buggy submission (status: Runtime Error):
// header {{{
// header {{{
using namespace std;
#include <bits/stdc++.h>

#define CPP_STR(x) CPP_STR_I(x)
#define CPP_CAT(x, y) CPP_CAT_I(x, y)
#define CPP_STR_I(args...) #args
#define CPP_CAT_I(x, y) x##y

#define ASSERT(expr...) assert((expr))

using i8 = int8_t;
using u8 = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;

using f32 = float;
using f64 = double;
// }}}

constexpr i64 INF = 1'010'000'000'000'000'017LL;

constexpr i64 MOD = 1'000'000'007LL;

constexpr f64 EPS = 1e-12;

constexpr f64 PI = 3.14159265358979323846;

#define M5 100007
#define M9 1000000000

// util {{{
#define FOR(i, start, end)                                                     \
  for (i64 i = (start), CPP_CAT(i, xxxx_end) = (end);                          \
       i < CPP_CAT(i, xxxx_end); ++i)
#define REP(i, n) FOR(i, 0, n)

#define ALL(f, c, ...)                                                         \
  (([&](decltype((c)) cccc) {                                                  \
    return (f)(std::begin(cccc), std::end(cccc), ##__VA_ARGS__);               \
  })(c))
#define ll long long int
#define VI vector<int>
template <typename C> i64 SIZE(const C &c) {
  return static_cast<i64>(c.size());
}

template <typename T, size_t N> i64 SIZE(const T (&)[N]) {
  return static_cast<i64>(N);
}

template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}
// }}}

// init {{{
struct ProconInit {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;

  ProconInit() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} PROCON_INIT;
// }}}

//--------------------------------------------------------------------

bool isOK(int mid, double key) {}

int binary_search(double key) {
  int left = -1; // 「index = 0」が条件を満たすこともあるので、初期値は -1
  int right = 2000000000;
  /* どんな二分探索でもここの書き方を変えずにできる！ */
  while (right - left > 1) {
    int mid = left + (right - left) / 2;

    if (isOK(mid, key))
      right = mid;
    else
      left = mid;
  }

  /* left は条件を満たさない最大の値、right は条件を満たす最小の値になっている
   */
  return right;
}

bool isKaibun(string st) {
  bool ans = true;
  int n = st.length();
  REP(i, n / 2) {
    if (st[i] != st[n - i - 1]) {
      return false;
    }
  }
  return true;
}

int toInt(char a) { return a - '0'; }

int gcd(int a, int b) {
  if (a % b == 0) {
    return (b);
  } else {
    return (gcd(b, a % b));
  }
}

int lcm(int a, int b) { return a * b / gcd(a, b); }

long long N;
string S;
int P;

long long solve() {
  cin >> S;
  N = S.length();
  P = 2019;
  vector<long long> val(P, 0);
  long long tenfactor = 1;
  long long cur = 0;
  val[cur]++;
  for (int i = 0; i < N; ++i) {
    cur = (cur + (S[N - i - 1] - '0') * tenfactor) % P;
    tenfactor = (tenfactor * 10) % P;
    val[cur]++;
  }
  long long res = 0;
  for (int p = 0; p < P; ++p)
    res += val[p] * (val[p] - 1) / 2;
  cout << res;
}
signed main() {

  solve();

  return 0;
}


Fixed submission:
// header {{{
// header {{{
using namespace std;
#include <bits/stdc++.h>

#define CPP_STR(x) CPP_STR_I(x)
#define CPP_CAT(x, y) CPP_CAT_I(x, y)
#define CPP_STR_I(args...) #args
#define CPP_CAT_I(x, y) x##y

#define ASSERT(expr...) assert((expr))

using i8 = int8_t;
using u8 = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;

using f32 = float;
using f64 = double;
// }}}

constexpr i64 INF = 1'010'000'000'000'000'017LL;

constexpr i64 MOD = 1'000'000'007LL;

constexpr f64 EPS = 1e-12;

constexpr f64 PI = 3.14159265358979323846;

#define M5 100007
#define M9 1000000000

// util {{{
#define FOR(i, start, end)                                                     \
  for (i64 i = (start), CPP_CAT(i, xxxx_end) = (end);                          \
       i < CPP_CAT(i, xxxx_end); ++i)
#define REP(i, n) FOR(i, 0, n)

#define ALL(f, c, ...)                                                         \
  (([&](decltype((c)) cccc) {                                                  \
    return (f)(std::begin(cccc), std::end(cccc), ##__VA_ARGS__);               \
  })(c))
#define ll long long int
#define VI vector<int>
template <typename C> i64 SIZE(const C &c) {
  return static_cast<i64>(c.size());
}

template <typename T, size_t N> i64 SIZE(const T (&)[N]) {
  return static_cast<i64>(N);
}

template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}
// }}}

// init {{{
struct ProconInit {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;

  ProconInit() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} PROCON_INIT;
// }}}

//--------------------------------------------------------------------

bool isOK(int mid, double key) {}

int binary_search(double key) {
  int left = -1; // 「index = 0」が条件を満たすこともあるので、初期値は -1
  int right = 2000000000;
  /* どんな二分探索でもここの書き方を変えずにできる！ */
  while (right - left > 1) {
    int mid = left + (right - left) / 2;

    if (isOK(mid, key))
      right = mid;
    else
      left = mid;
  }

  /* left は条件を満たさない最大の値、right は条件を満たす最小の値になっている
   */
  return right;
}

bool isKaibun(string st) {
  bool ans = true;
  int n = st.length();
  REP(i, n / 2) {
    if (st[i] != st[n - i - 1]) {
      return false;
    }
  }
  return true;
}

int toInt(char a) { return a - '0'; }

int gcd(int a, int b) {
  if (a % b == 0) {
    return (b);
  } else {
    return (gcd(b, a % b));
  }
}

int lcm(int a, int b) { return a * b / gcd(a, b); }

long long N;
string S;
int P;

void solve() {
  cin >> S;
  N = S.length();
  P = 2019;
  vector<long long> val(P, 0);
  long long tenfactor = 1;
  long long cur = 0;
  val[cur]++;
  for (int i = 0; i < N; ++i) {
    cur = (cur + (S[N - i - 1] - '0') * tenfactor) % P;
    tenfactor = (tenfactor * 10) % P;
    val[cur]++;
  }
  long long res = 0;
  for (int p = 0; p < P; ++p)
    res += val[p] * (val[p] - 1) / 2;
  cout << res;
}
signed main() {

  solve();

  return 0;
}