Problem p02840 (C++)

Buggy submission (status: Runtime Error):
// template version 1.14
using namespace std;
#include <bits/stdc++.h>

// varibable settings
#define int long long
const int INF = 1e18;
const int MOD = 1e9 + 7;

// define basic macro {{{
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define _rrep(i, n) rrepi(i, 0, n)
#define rrepi(i, a, b) for (int i = (int)((b)-1); i >= (int)(a); --i)
#define rrep(...) _overload3(__VA_ARGS__, rrepi, _rrep, )(__VA_ARGS__)
#define each(i, a) for (auto &&i : a)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define mt(a, b, c) make_tuple(a, b, c)
#define ceil(a, b) ((a) + (b)-1) / (b)
#define is_in(x, a, b) ((a) <= (x) && (x) < (b))
#define uni(x)                                                                 \
  sort(all(x));                                                                \
  x.erase(unique(all(x)), x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x) - A.begin())
#define posu(A, x) (upper_bound(all(A), x) - A.begin())
template <class T> inline void chmax(T &a, const T &b) {
  if ((a) < (b))
    (a) = (b);
}
template <class T> inline void chmin(T &a, const T &b) {
  if ((a) > (b))
    (a) = (b);
}

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int, int> pii;
typedef tuple<int, int, int> iii;

template <typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast {
  Fast() {
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;

#if defined(PCM) || defined(LOCAL)
#include "lib/dump.hpp"
#else
#define dump(...) 42
#define dump_1d(...) 42
#define dump_2d(...) 42
#endif
//}}}

signed main() {
  int n, x, d;
  cin >> n >> x >> d;
  map<int, vector<pii>> z;
  int ans = 0;

  if (d < 0) {
    int last = x + (n - 1) * d;
    x = last;
    d = -d;
  }
  dump(x, d);

  int l = 0;
  int r = 0;
  rep(a, 0, n + 1) {
    int add = (a * x) / d;
    int rem = (a * x) % d;
    if (rem < 0) {
      rem += d;
      add -= 1;
    }
    dump(a, l, r);

    ans += r - l + 1;
    if (sz(z[rem]) > 0) {
      auto tmp = *(z[rem].rbegin());
      int preladd = tmp.first;
      int preradd = tmp.second;
      int dec = max(0LL, min(add + r, preradd) - max(add + l, preladd) + 1);
      dump(preladd, preradd, add + l, add + r, dec);
      ans -= dec;
    }
    z[rem].pb(mp(add + l, add + r));

    l += a;
    r += n - (a + 1);
  }
  dump(z);
  cout << ans << endl;
  return 0;
}


Fixed submission:
// template version 1.14
using namespace std;
#include <bits/stdc++.h>

// varibable settings
#define int long long
const int INF = 1e18;
const int MOD = 1e9 + 7;

// define basic macro {{{
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep, )(__VA_ARGS__)
#define _rrep(i, n) rrepi(i, 0, n)
#define rrepi(i, a, b) for (int i = (int)((b)-1); i >= (int)(a); --i)
#define rrep(...) _overload3(__VA_ARGS__, rrepi, _rrep, )(__VA_ARGS__)
#define each(i, a) for (auto &&i : a)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define mt(a, b, c) make_tuple(a, b, c)
#define ceil(a, b) ((a) + (b)-1) / (b)
#define is_in(x, a, b) ((a) <= (x) && (x) < (b))
#define uni(x)                                                                 \
  sort(all(x));                                                                \
  x.erase(unique(all(x)), x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x) - A.begin())
#define posu(A, x) (upper_bound(all(A), x) - A.begin())
template <class T> inline void chmax(T &a, const T &b) {
  if ((a) < (b))
    (a) = (b);
}
template <class T> inline void chmin(T &a, const T &b) {
  if ((a) > (b))
    (a) = (b);
}

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int, int> pii;
typedef tuple<int, int, int> iii;

template <typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast {
  Fast() {
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;

#if defined(PCM) || defined(LOCAL)
#include "lib/dump.hpp"
#else
#define dump(...) 42
#define dump_1d(...) 42
#define dump_2d(...) 42
#endif
//}}}

signed main() {
  int n, x, d;
  cin >> n >> x >> d;
  map<int, vector<pii>> z;
  int ans = 0;

  if (x == 0 && d == 0) {
    cout << 1 << endl;
    return 0;
  }

  if (d == 0) {
    cout << n + 1 << endl;
    return 0;
  }

  if (d < 0) {
    int last = x + (n - 1) * d;
    x = last;
    d = -d;
  }
  dump(x, d);

  int l = 0;
  int r = 0;
  rep(a, 0, n + 1) {
    int add = (a * x) / d;
    int rem = (a * x) % d;
    if (rem < 0) {
      rem += d;
      add -= 1;
    }
    dump(a, l, r);

    ans += r - l + 1;
    if (sz(z[rem]) > 0) {
      auto tmp = *(z[rem].rbegin());
      int preladd = tmp.first;
      int preradd = tmp.second;
      int dec = max(0LL, min(add + r, preradd) - max(add + l, preladd) + 1);
      dump(preladd, preradd, add + l, add + r, dec);
      ans -= dec;
    }
    z[rem].pb(mp(add + l, add + r));

    l += a;
    r += n - (a + 1);
  }
  dump(z);
  cout << ans << endl;
  return 0;
}