Problem p02788 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
typedef long long int ll;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; PPPPP(__VA_ARGS__); cerr << endl; } while(false)
template<typename T> void PPPPP(T t) { cerr << t; }
template<typename T, typename... S> void PPPPP(T t, S... s) { cerr << t << ", "; PPPPP(s...); }
#else
#define dump(...)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T>
bool chmin(T &a, T b) { if (a > b) {a = b; return true; } return false;}
template<typename T>
bool chmax(T &a, T b) { if (a < b) {a = b; return true; } return false;}
// clang-format on

#include <functional>
template <typename T> class SegmentTreeAllOne {
  using Func = function<T(T, T)>;

public:
  vector<T> data;
  int n;
  T init;
  Func update_func;
  SegmentTreeAllOne(int _n, T _init, Func up) {
    init = _init;
    update_func = up;
    for (n = 1; n < _n; n *= 2)
      ;
    data.resize(2 * n - 1, init);
  }
  void update(int l, int r, T val) {
    for (l += n - 1, r += n - 1; l < r; l = l / 2, r = (r - 1) / 2) {
      if (!(l & 1)) {
        data[l] = update_func(data[l], val);
      }
      if (!(r & 1)) {
        data[r - 1] = update_func(data[r - 1], val);
      }
    }
  }
  T query(int pos) {
    pos += n - 1;
    T res = data[pos];
    while (pos > 0) {
      pos = (pos - 1) / 2;
      res = update_func(res, data[pos]);
    }
    return res;
  }
};

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  ll n, d, a;
  cin >> n >> d >> a;
  vector<ll> x(n), h(n);
  REP(i, 0, n) { cin >> x[i] >> h[i]; }
  vector<int> ord(n);
  iota(ord.begin(), ord.end(), 0);
  sort(ord.begin(), ord.end(), [&](int t, int s) {
    if (x[t] != x[s])
      return x[t] < x[s];
    else
      return h[t] < h[s];
  });
  auto sum = [](ll t, ll s) { return t + s; };
  SegmentTreeAllOne<ll> segtree(n, 0LL, sum);

  ll cnt = 0;
  int p = 0;
  REP(i, 0, n) {
    ll res = h[ord[i]] - segtree.query(i);
    if (res <= 0)
      continue;
    while (p < n && x[ord[p]] - 2 * d <= x[ord[i]]) {
      p++;
    }
    ll cn = (res + a - 1) / a;
    segtree.update(x[ord[i]], x[ord[p - 1]], cn * a);
    cnt += cn;
  }

  cout << cnt << endl;
  return 0;
}


Fixed submission:
#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
typedef long long int ll;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; PPPPP(__VA_ARGS__); cerr << endl; } while(false)
template<typename T> void PPPPP(T t) { cerr << t; }
template<typename T, typename... S> void PPPPP(T t, S... s) { cerr << t << ", "; PPPPP(s...); }
#else
#define dump(...)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T>
bool chmin(T &a, T b) { if (a > b) {a = b; return true; } return false;}
template<typename T>
bool chmax(T &a, T b) { if (a < b) {a = b; return true; } return false;}
// clang-format on

#include <functional>
template <typename T> class SegmentTreeAllOne {
  using Func = function<T(T, T)>;

public:
  vector<T> data;
  int n;
  T init;
  Func update_func;
  SegmentTreeAllOne(int _n, T _init, Func up) {
    init = _init;
    update_func = up;
    for (n = 1; n < _n; n *= 2)
      ;
    data.resize(2 * n - 1, init);
  }
  void update(int l, int r, T val) {
    for (l += n - 1, r += n - 1; l < r; l = l / 2, r = (r - 1) / 2) {
      if (!(l & 1)) {
        data[l] = update_func(data[l], val);
      }
      if (!(r & 1)) {
        data[r - 1] = update_func(data[r - 1], val);
      }
    }
  }
  T query(int pos) {
    pos += n - 1;
    T res = data[pos];
    while (pos > 0) {
      pos = (pos - 1) / 2;
      res = update_func(res, data[pos]);
    }
    return res;
  }
};

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  ll n, d, a;
  cin >> n >> d >> a;
  vector<ll> x(n), h(n);
  REP(i, 0, n) { cin >> x[i] >> h[i]; }
  vector<int> ord(n);
  iota(ord.begin(), ord.end(), 0);
  sort(ord.begin(), ord.end(), [&](int t, int s) {
    if (x[t] != x[s])
      return x[t] < x[s];
    else
      return h[t] < h[s];
  });
  auto sum = [](ll t, ll s) { return t + s; };
  SegmentTreeAllOne<ll> segtree(n, 0LL, sum);

  ll cnt = 0;
  int p = 0;
  REP(i, 0, n) {
    ll res = h[ord[i]] - segtree.query(i);
    if (res <= 0)
      continue;
    while (p < n && x[ord[p]] - 2 * d <= x[ord[i]]) {
      p++;
    }
    ll cn = (res + a - 1) / a;
    segtree.update(i, p, cn * a);
    cnt += cn;
  }

  cout << cnt << endl;
  return 0;
}