Problem p03785 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define dump(x)                                                                \
  if (dbg) {                                                                   \
    cerr << #x << " = " << (x) << endl;                                        \
  }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  } else
    return 0;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  } else
    return 0;
}
void Yes(bool flag = true) {
  if (flag)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
void No(bool flag = true) { Yes(!flag); }
void YES(bool flag = true) {
  if (flag)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void NO(bool flag = true) { YES(!flag); }
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
bool dbg = false;
} // namespace mydef
using namespace mydef;
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
// #define P pair<int, int>
// #define V vector<int>
// #define S set<int>
#define asn ans

int N, C, K, T[101010];

void solve() {}

signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);

  cin >> N >> C >> K;
  for (int i = 0; i < N; i++) {
    cin >> T[i];
  }
  sort(T, T + N);
  int ans = 0;
  for (int i = 0; i < N;) {
    ans++;
    int start = i;
    while (T[i] - T[start] <= K && i - start < C)
      i++;
  }
  cout << ans << endl;

  solve();
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define dump(x)                                                                \
  if (dbg) {                                                                   \
    cerr << #x << " = " << (x) << endl;                                        \
  }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  } else
    return 0;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  } else
    return 0;
}
void Yes(bool flag = true) {
  if (flag)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
void No(bool flag = true) { Yes(!flag); }
void YES(bool flag = true) {
  if (flag)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void NO(bool flag = true) { YES(!flag); }
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
bool dbg = false;
} // namespace mydef
using namespace mydef;
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
// #define P pair<int, int>
// #define V vector<int>
// #define S set<int>
#define asn ans

int N, C, K, T[101010];

void solve() {}

signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);

  cin >> N >> C >> K;
  for (int i = 0; i < N; i++) {
    cin >> T[i];
  }
  sort(T, T + N);
  int ans = 0;
  for (int i = 0; i < N;) {
    ans++;
    int start = i;
    while (i < N && T[i] - T[start] <= K && i - start < C)
      i++;
  }
  cout << ans << endl;

  solve();
  return 0;
}