Problem p02840 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf = 1e9 + 7;
const ll INF = 1LL << 60;
const ll mod = 1e9 + 7;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(), c.end()
#define pb push_back
#define debug(x) cout << #x << " = " << (x) << endl;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
#define int long long

void solve() {
  int n, x, d;
  cin >> n >> x >> d;
  static map<int, vector<pair<int, int>>> mp;
  for (int k = 0; k <= n; ++k) {
    int a = x * k % d, b = x * k / d;
    int p = b + k * (k - 1) / 2, q = b + k * (2 * n - k - 1) / 2;
    if (p > q)
      swap(p, q);
    mp[a].push_back(make_pair(p, q + 1));
  }
  int ans = 0;
  for (auto &X : mp) {
    auto vec = X.sc;
    sort(all(vec));
    int l = vec[0].fr, r = vec[0].sc;
    for (auto &ra : vec) {
      int p = ra.fr, q = ra.sc;
      if (p <= r) {
        r = max(r, q);
      } else {
        ans += r - l;
        l = p, r = q;
      }
    }
    ans += r - l;
  }
  cout << ans << endl;
}

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  // cout << fixed << setprecision(10);
  // init();
  solve();
  // cout << "finish" << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf = 1e9 + 7;
const ll INF = 1LL << 60;
const ll mod = 1e9 + 7;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(), c.end()
#define pb push_back
#define debug(x) cout << #x << " = " << (x) << endl;
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
#define int long long

void solve() {
  int n, x, d;
  cin >> n >> x >> d;
  if (x == 0 && d == 0) {
    cout << 1 << endl;
    return;
  }
  if (d == 0) {
    cout << n + 1 << endl;
    return;
  }
  static map<int, vector<pair<int, int>>> mp;
  for (int k = 0; k <= n; ++k) {
    int a = x * k % d, b = x * k / d;
    int p = b + k * (k - 1) / 2, q = b + k * (2 * n - k - 1) / 2;
    if (p > q)
      swap(p, q);
    mp[a].push_back(make_pair(p, q + 1));
  }
  int ans = 0;
  for (auto &X : mp) {
    auto vec = X.sc;
    sort(all(vec));
    int l = vec[0].fr, r = vec[0].sc;
    for (auto &ra : vec) {
      int p = ra.fr, q = ra.sc;
      if (p <= r) {
        r = max(r, q);
      } else {
        ans += r - l;
        l = p, r = q;
      }
    }
    ans += r - l;
  }
  cout << ans << endl;
}

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  // cout << fixed << setprecision(10);
  // init();
  solve();
  // cout << "finish" << endl;
  return 0;
}