Problem p03785 (C++)

Buggy submission (status: Runtime Error):
/* ---------- STL Libraries ---------- */

// IO library
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>

// container library
#include <deque>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

/* ---------- Namespace ---------- */

using namespace std;

/* ---------- Type Abbreviation ---------- */

template <typename T> using V = vector<T>;
template <typename T, typename U> using P = pair<T, U>;

using ll = long long;
using PL = P<ll, ll>;
using PS = P<string, ll>;

using VI = V<int>;
using VVI = V<VI>;
using VL = V<ll>;
using VVL = V<VL>;
using VS = V<string>;
using VB = V<bool>;
using VVB = V<VB>;
using VPL = V<PL>;
using VPS = V<PS>;

#define fst first
#define snd second

/* ---------- conversion ---------- */

#define INT(c) static_cast<int>(c)
#define CHAR(n) static_cast<char>(n)
#define LL(n) static_cast<ll>(n)
#define DOUBLE(n) static_cast<double>(n)

/* ---------- container ---------- */

#define EACH(i, c) for (auto i = (c).begin(); i != (c).end(); i++)
#define ALL(c) (c).begin(), (c).end()
#define SORT(c) sort(ALL(c))
#define GSORT(c) sort(ALL(c), greater<decltype((c).front())>())
#define SZ(x) (LL((x).size()))

/* ---------- repetition ---------- */

#define FOR(i, a, b) for (ll i = (a); i <= (b); i++)
#define REP(i, n) FOR(i, 0, n - 1)
#define NREP(i, n) FOR(i, 1, n)

#define RFOR(i, a, b) for (ll i = (a); i >= (b); i--)
#define RREP(i, n) RFOR(i, n, 0)
#define RNREP(i, n) RFOR(i, n, 1)

// Usual REP runs from 0 to n-1 (R: n to 0)
// Natural REP runs from 1 to n (R: n to 1)

/* ---------- Constants ---------- */

// const ll MOD = 1e9 + 7;
// const int INF = 1 << 25;
const ll INF = 1LL << 50;
// const double PI = 3.14159265358979;
// const ll dx[4] = {0, -1, 1, 0};
// const ll dy[4] = {-1, 0, 0, 1};
// const ll dx[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
// const ll dy[8] = {-1, -1, -1, 0, 0, 1, 1, 1};

/* ---------- Short Functions ---------- */

template <typename T> T square(T a) { return a * a; }

/* ---------- Debug ---------- */
#define GET_VAR_NAME(variable) #variable

#define test(x) cout << GET_VAR_NAME(x) << " = " << x << endl;
#define testP(p)                                                               \
  cout << GET_VAR_NAME(p) << " = (" << (p).fst << ", " << (p).snd << ")"       \
       << endl;

/* ^^^^^^^^^^^^^^^ Settting Part ^^^^^^^^^^^^^^^ */

/* ---------- Variances ---------- */

/* ---------- Functions ---------- */

/* ---------- Main Function ---------- */

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N, C, K;
  cin >> N >> C >> K;

  VL T(N);
  REP(i, N) { cin >> T[i]; }
  T[N] = INF;

  SORT(T);

  ll ans = 0;
  ll itr = 0;
  while (true) {
    ll limit = T[itr] + K;
    ll cus_num = 1;

    itr++;

    while (true) {
      if (T[itr] <= limit && cus_num < C) {
        // cout << itr << " took." << endl;
        cus_num++;
        itr++;
      } else {
        // cout << itr << " excluded." << endl;
        ans++;
        break;
      }
    }

    if (itr == N) {
      break;
    }
  }

  cout << ans << endl;
  return 0;
}

Fixed submission:
/* ---------- STL Libraries ---------- */

// IO library
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>

// container library
#include <deque>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

/* ---------- Namespace ---------- */

using namespace std;

/* ---------- Type Abbreviation ---------- */

template <typename T> using V = vector<T>;
template <typename T, typename U> using P = pair<T, U>;

using ll = long long;
using PL = P<ll, ll>;
using PS = P<string, ll>;

using VI = V<int>;
using VVI = V<VI>;
using VL = V<ll>;
using VVL = V<VL>;
using VS = V<string>;
using VB = V<bool>;
using VVB = V<VB>;
using VPL = V<PL>;
using VPS = V<PS>;

#define fst first
#define snd second

/* ---------- conversion ---------- */

#define INT(c) static_cast<int>(c)
#define CHAR(n) static_cast<char>(n)
#define LL(n) static_cast<ll>(n)
#define DOUBLE(n) static_cast<double>(n)

/* ---------- container ---------- */

#define EACH(i, c) for (auto i = (c).begin(); i != (c).end(); i++)
#define ALL(c) (c).begin(), (c).end()
#define SORT(c) sort(ALL(c))
#define GSORT(c) sort(ALL(c), greater<decltype((c).front())>())
#define SZ(x) (LL((x).size()))

/* ---------- repetition ---------- */

#define FOR(i, a, b) for (ll i = (a); i <= (b); i++)
#define REP(i, n) FOR(i, 0, n - 1)
#define NREP(i, n) FOR(i, 1, n)

#define RFOR(i, a, b) for (ll i = (a); i >= (b); i--)
#define RREP(i, n) RFOR(i, n, 0)
#define RNREP(i, n) RFOR(i, n, 1)

// Usual REP runs from 0 to n-1 (R: n to 0)
// Natural REP runs from 1 to n (R: n to 1)

/* ---------- Constants ---------- */

// const ll MOD = 1e9 + 7;
// const int INF = 1 << 25;
const ll INF = 1LL << 50;
// const double PI = 3.14159265358979;
// const ll dx[4] = {0, -1, 1, 0};
// const ll dy[4] = {-1, 0, 0, 1};
// const ll dx[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
// const ll dy[8] = {-1, -1, -1, 0, 0, 1, 1, 1};

/* ---------- Short Functions ---------- */

template <typename T> T square(T a) { return a * a; }

/* ---------- Debug ---------- */
#define GET_VAR_NAME(variable) #variable

#define test(x) cout << GET_VAR_NAME(x) << " = " << x << endl;
#define testP(p)                                                               \
  cout << GET_VAR_NAME(p) << " = (" << (p).fst << ", " << (p).snd << ")"       \
       << endl;

/* ^^^^^^^^^^^^^^^ Settting Part ^^^^^^^^^^^^^^^ */

/* ---------- Variances ---------- */

/* ---------- Functions ---------- */

/* ---------- Main Function ---------- */

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N, C, K;
  cin >> N >> C >> K;

  VL T(N + 1);
  REP(i, N) { cin >> T[i]; }
  T[N] = INF;

  SORT(T);

  ll ans = 0;
  ll itr = 0;
  while (true) {
    ll limit = T[itr] + K;
    ll cus_num = 1;

    itr++;

    while (true) {
      if (T[itr] <= limit && cus_num < C) {
        // cout << itr << " took." << endl;
        cus_num++;
        itr++;
      } else {
        // cout << itr << " excluded." << endl;
        ans++;
        break;
      }
    }

    if (itr == N) {
      break;
    }
  }

  cout << ans << endl;
  return 0;
}