In this problem, we're asked the minimum number of rooms needed to accommodate $n$ customers, which arrive and leave on set days.

Main Idea

• First Step: Sort by arrival time (we cannot have a customer arriving at say, time 3, occupying a room before a customer arriving at time 2).
• Second Step: Maintain a minimum heap which stores the time a hotel room will be unoccupied.
  • Every time a new customer arrvies, we check to see if the minimum element in the heap is less than the arrival time of the new customer.
  • If this is true, we can just switch the times.
  • If not, then we need to add another room to the heap.

1#include <iostream>
2#include <algorithm>
3#include <queue>
4using namespace std;
5
6
7int N;
8int ans[200005];
9vector<pair<pair<int, int>, int> > v(200005);
10