Problem p02840 (C++)

Buggy submission (status: Runtime Error):
#pragma region
#include <bits/stdc++.h>
using namespace std;
/*
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
*/
#define int long long
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; i--)
#define FOR(i, s, n) for (int i = s; i < (int)n; i++)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; i--)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template <class T> inline bool CHMAX(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool CHMIN(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <class T> inline void in(T &t) { cin >> t; }
template <class T, class... Ts> inline void in(T &t, Ts &...ts) {
  cin >> t;
  in(ts...);
}
template <class T> inline void out(T t) { cout << t << endl; }
template <class T, class... Ts> inline void out(T t, Ts... ts) {
  cout << t << " ";
  out(ts...);
}
template <typename T = int> vector<T> mv(size_t a) { return vector<T>(a); }
template <typename T = int, typename... Ts> auto mv(size_t a, Ts... ts) {
  return vector<decltype(mv<T>(ts...))>(a, mv<T>(ts...));
}
template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill(T &t, const V &v) {
  t = v;
}
template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill(T &t, const V &v) {
  for (auto &e : t)
    fill(e, v);
}
constexpr long long INF = 1e18;

template <int MOD> struct Fp {
  long long val;
  constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  constexpr int getmod() { return MOD; }
  constexpr Fp operator-() const noexcept { return val ? MOD - val : 0; }
  constexpr Fp operator+(const Fp &r) const noexcept { return Fp(*this) += r; }
  constexpr Fp operator-(const Fp &r) const noexcept { return Fp(*this) -= r; }
  constexpr Fp operator*(const Fp &r) const noexcept { return Fp(*this) *= r; }
  constexpr Fp operator/(const Fp &r) const noexcept { return Fp(*this) /= r; }
  constexpr Fp &operator+=(const Fp &r) noexcept {
    val += r.val;
    if (val >= MOD)
      val -= MOD;
    return *this;
  }
  constexpr Fp &operator-=(const Fp &r) noexcept {
    val -= r.val;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr Fp &operator*=(const Fp &r) noexcept {
    val = val * r.val % MOD;
    return *this;
  }
  constexpr Fp &operator/=(const Fp &r) noexcept {
    long long a = r.val, b = MOD, u = 1, v = 0;
    while (b) {
      long long t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr bool operator==(const Fp &r) const noexcept {
    return this->val == r.val;
  }
  constexpr bool operator!=(const Fp &r) const noexcept {
    return this->val != r.val;
  }
  friend constexpr ostream &operator<<(ostream &os, const Fp<MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};

// 二項係数ライブラリ
template <class T> struct BiCoef {
  vector<T> fact_, inv_, finv_;
  constexpr BiCoef() {}
  constexpr BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    int MOD = fact_[0].getmod();
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T com(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
};

const int MOD = 1000000007;
// const int MOD = 998244353;
using mint = Fp<MOD>;
BiCoef<mint> bc;
// bc.init(500050);
#pragma endregion

signed main() {
  int N, X, D;
  in(N, X, D);
  int ans = 0;
  int right = 0;
  int left = 0;
  map<int, vector<pair<int, int>>> mp; // modDを区間で管理
  mp[0].emplace_back(0, 0);
  REP(i, N) {
    right += N - i - 1;
    left += i;
    int mo = X * (i + 1) % D;
    int l = left + X * (i + 1) / D;
    int r = right + X * (i + 1) / D;
    mp[mo].emplace_back(l, r);
  }
  for (auto m : mp) {
    auto v = m.second;
    sort(ALL(v));
    int l = v[0].first, r = v[0].second;
    FOR(i, 1, v.size()) {
      if (r < v[i].first) {
        ans += r - l + 1;
        l = v[i].first;
        r = v[i].second;
      } else {
        CHMAX(r, v[i].second);
      }
    }
    ans += r - l + 1;
  }
  out(ans);
}

Fixed submission:
#pragma region
#include <bits/stdc++.h>
using namespace std;
/*
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
*/
#define int long long
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; i--)
#define FOR(i, s, n) for (int i = s; i < (int)n; i++)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; i--)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template <class T> inline bool CHMAX(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool CHMIN(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <class T> inline void in(T &t) { cin >> t; }
template <class T, class... Ts> inline void in(T &t, Ts &...ts) {
  cin >> t;
  in(ts...);
}
template <class T> inline void out(T t) { cout << t << endl; }
template <class T, class... Ts> inline void out(T t, Ts... ts) {
  cout << t << " ";
  out(ts...);
}
template <typename T = int> vector<T> mv(size_t a) { return vector<T>(a); }
template <typename T = int, typename... Ts> auto mv(size_t a, Ts... ts) {
  return vector<decltype(mv<T>(ts...))>(a, mv<T>(ts...));
}
template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill(T &t, const V &v) {
  t = v;
}
template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill(T &t, const V &v) {
  for (auto &e : t)
    fill(e, v);
}
constexpr long long INF = 1e18;

template <int MOD> struct Fp {
  long long val;
  constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  constexpr int getmod() { return MOD; }
  constexpr Fp operator-() const noexcept { return val ? MOD - val : 0; }
  constexpr Fp operator+(const Fp &r) const noexcept { return Fp(*this) += r; }
  constexpr Fp operator-(const Fp &r) const noexcept { return Fp(*this) -= r; }
  constexpr Fp operator*(const Fp &r) const noexcept { return Fp(*this) *= r; }
  constexpr Fp operator/(const Fp &r) const noexcept { return Fp(*this) /= r; }
  constexpr Fp &operator+=(const Fp &r) noexcept {
    val += r.val;
    if (val >= MOD)
      val -= MOD;
    return *this;
  }
  constexpr Fp &operator-=(const Fp &r) noexcept {
    val -= r.val;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr Fp &operator*=(const Fp &r) noexcept {
    val = val * r.val % MOD;
    return *this;
  }
  constexpr Fp &operator/=(const Fp &r) noexcept {
    long long a = r.val, b = MOD, u = 1, v = 0;
    while (b) {
      long long t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  constexpr bool operator==(const Fp &r) const noexcept {
    return this->val == r.val;
  }
  constexpr bool operator!=(const Fp &r) const noexcept {
    return this->val != r.val;
  }
  friend constexpr ostream &operator<<(ostream &os, const Fp<MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};

// 二項係数ライブラリ
template <class T> struct BiCoef {
  vector<T> fact_, inv_, finv_;
  constexpr BiCoef() {}
  constexpr BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    int MOD = fact_[0].getmod();
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T com(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
};

const int MOD = 1000000007;
// const int MOD = 998244353;
using mint = Fp<MOD>;
BiCoef<mint> bc;
// bc.init(500050);
#pragma endregion

signed main() {
  int N, X, D;
  in(N, X, D);
  int ans = 0;
  int right = 0;
  int left = 0;
  map<int, vector<pair<int, int>>> mp; // modDを区間で管理
  mp[0].emplace_back(0, 0);
  REP(i, N) {
    right += N - i - 1;
    left += i;
    if (D) {
      int mo = X * (i + 1) % D;
      int l = left + X * (i + 1) / D;
      int r = right + X * (i + 1) / D;
      mp[mo].emplace_back(l, r);
    } else {
      int l = X * (i + 1);
      int r = X * (i + 1);
      mp[0].emplace_back(l, r);
    }
  }
  for (auto m : mp) {
    auto v = m.second;
    sort(ALL(v));
    int l = v[0].first, r = v[0].second;
    FOR(i, 1, v.size()) {
      if (r < v[i].first) {
        ans += r - l + 1;
        l = v[i].first;
        r = v[i].second;
      } else {
        CHMAX(r, v[i].second);
      }
    }
    ans += r - l + 1;
  }
  out(ans);
}