Problem p02788 (C++)

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

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;
typedef vector<ld> vld;
typedef vector<pll> vpll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n, d, a;
  cin >> n >> d >> a;
  vll x(n), h(n);
  REP(i, n) cin >> x[i] >> h[i];

  vector<pll> p(n);
  REP(i, n) {
    p[i].FI = x[i];
    p[i].SE = h[i];
  }

  map<ll, ll> m;
  sort(x.begin(), x.end());
  sort(p.begin(), p.end());
  REP(i, n)
  m[p[i].FI] = i;

  ll ans = 0;
  vll imos(n, 0);

  REP(i, n) {
    ll health = p[i].SE;
    if (i != 0)
      imos[i] += imos[i - 1];
    health -= imos[i] * a;

    if (health <= 0)
      continue;

    auto it = upper_bound(x.begin(), x.end(), x[i] + 2 * d);
    ll t = it - x.begin();

    ll k = health / a;
    if (health % a != 0)
      k++;

    imos[i] += k;
    imos[t] -= k;

    ans += k;
  }

  cout << ans << endl;
}


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

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;
typedef vector<ld> vld;
typedef vector<pll> vpll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n, d, a;
  cin >> n >> d >> a;
  vll x(n), h(n);
  REP(i, n) cin >> x[i] >> h[i];

  vector<pll> p(n);
  REP(i, n) {
    p[i].FI = x[i];
    p[i].SE = h[i];
  }

  map<ll, ll> m;
  sort(x.begin(), x.end());
  sort(p.begin(), p.end());
  REP(i, n)
  m[p[i].FI] = i;

  ll ans = 0;
  vll imos(n + 2, 0);

  REP(i, n) {
    ll health = p[i].SE;
    if (i != 0)
      imos[i] += imos[i - 1];
    health -= imos[i] * a;

    if (health <= 0)
      continue;

    auto it = upper_bound(x.begin(), x.end(), x[i] + 2 * d);
    ll t = it - x.begin();

    ll k = health / a;
    if (health % a != 0)
      k++;

    imos[i] += k;
    imos[t] -= k;

    ans += k;
  }

  cout << ans << endl;
}