Problem p02948 (C++)

Buggy submission (status: Runtime Error):
/*
    Author:zeke

    pass System Test!
    GET AC!!
*/
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using ll = long long;
using ld = long double;
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define rep3(var, min, max) for (ll(var) = (min); (var) < (max); ++(var))
#define repi3(var, min, max) for (ll(var) = (max)-1; (var) + 1 > (min); --(var))
#define Mp(a, b) make_pair((a), (b))
#define F first
#define S second
#define Icin(s)                                                                \
  ll(s);                                                                       \
  cin >> (s);
#define Scin(s)                                                                \
  ll(s);                                                                       \
  cin >> (s);
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;
}
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<V> VV;
typedef vector<P> VP;
ll mod = 1e9 + 7;
ll MOD = 1e9 + 7;
ll INF = 1e18;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, m;
  cin >> n >> m;
  VV vec(m);
  rep(i, n) {
    ll a, b;
    cin >> a >> b;
    a--;
    if (a >= n)
      continue;
    vec[a].push_back(b);
  }
  priority_queue<ll> q;
  ll sum = 0;
  rep(i, m) {
    rep(j, vec[i].size()) { q.push(vec[i][j]); }
    if (!q.empty()) {
      sum += q.top();
      q.pop();
    }
  }
  cout << sum << endl;
}


Fixed submission:
/*
    Author:zeke

    pass System Test!
    GET AC!!
*/
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using ll = long long;
using ld = long double;
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define rep3(var, min, max) for (ll(var) = (min); (var) < (max); ++(var))
#define repi3(var, min, max) for (ll(var) = (max)-1; (var) + 1 > (min); --(var))
#define Mp(a, b) make_pair((a), (b))
#define F first
#define S second
#define Icin(s)                                                                \
  ll(s);                                                                       \
  cin >> (s);
#define Scin(s)                                                                \
  ll(s);                                                                       \
  cin >> (s);
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;
}
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<V> VV;
typedef vector<P> VP;
ll mod = 1e9 + 7;
ll MOD = 1e9 + 7;
ll INF = 1e18;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, m;
  cin >> n >> m;
  VV vec(m);
  rep(i, n) {
    ll a, b;
    cin >> a >> b;
    a--;
    if (a >= m)
      continue;
    vec[a].push_back(b);
  }
  priority_queue<ll> q;
  ll sum = 0;
  rep(i, m) {
    rep(j, vec[i].size()) { q.push(vec[i][j]); }
    if (!q.empty()) {
      sum += q.top();
      q.pop();
    }
  }
  cout << sum << endl;
}