Problem p03785 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#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) for (int i = (n - 1); i >= 0; i--)
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define MAX(v) *max_element(all(v))
#define MIN(v) *min_element(all(v))
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vl = vector<ll>;
using vvl = vector<vl>;
void debug_out() { cout << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
inline void IN(void) { return; }
template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, c, k;
  IN(n, c, k);
  vector<ll> t(n);
  rep(i, n) cin >> t[i];
  vl s(MAX(t) + k + 2);
  rep(i, n) {
    s[t[i]]++;
    s[t[i] + k + 1]--;
  }
  rep(i, MAX(t) + k) s[i + 1] += s[i];
  ll ans = -1;
  rep(i, MAX(t) + k + 2) {
    if (s[i + 1] < s[i])
      ans++;
  }
  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
#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) for (int i = (n - 1); i >= 0; i--)
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define MAX(v) *max_element(all(v))
#define MIN(v) *min_element(all(v))
using namespace std;
using ll = long long;
using P = pair<int, int>;
using vl = vector<ll>;
using vvl = vector<vl>;
void debug_out() { cout << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cout << H << " ";
  debug_out(T...);
}
#ifdef _DEBUG
#define debug(...) debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
inline void IN(void) { return; }
template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, c, k;
  IN(n, c, k);
  vector<ll> t(n);
  rep(i, n) cin >> t[i];
  sort(all(t));
  ll ans = 0;
  // 乗せる人の添字の範囲
  ll left = 0;
  ll right = 0;
  while (right < n) {
    while (right - left + 1 < c && right < n - 1 && t[right + 1] <= t[left] + k)
      right++;
    ans++;
    left = right + 1;
    right++;
  }
  cout << ans << endl;
}