백준 11000 강의실배정

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <queue>
using namespace std;

vector<pair<int, int>> times;
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int N; cin>>N;
    times.resize(N);
    for(auto &time:times){
        cin>>time.first>>time.second;
    }
    sort(times.begin(), times.end());

    priority_queue<int, vector<int>, greater<int>> rooms;

    for(auto &time:times){
        if(rooms.empty()){
            rooms.push(time.second);
            continue;
        }
        int top=rooms.top();
        if(top<=time.first) {
            rooms.pop();
            rooms.push(time.second);
        }
        else
            rooms.push(time.second);
    }
    cout<<rooms.size();
    //std::cout << "Hello, World!" << std::endl;
    return 0;
}