<p>You are given an integer <code>n</code>. There are <code>n</code> rooms numbered from <code>0</code> to <code>n - 1</code>.</p>

<p>You are given a 2D integer array <code>meetings</code> where <code>meetings[i] = [start<sub>i</sub>, end<sub>i</sub>]</code> means that a meeting will be held during the <strong>half-closed</strong> time interval <code>[start<sub>i</sub>, end<sub>i</sub>)</code>. All the values of <code>start<sub>i</sub></code> are <strong>unique</strong>.</p>

<p>Meetings are allocated to rooms in the following manner:</p>

<ol>
	<li>Each meeting will take place in the unused room with the <strong>lowest</strong> number.</li>
	<li>If there are no available rooms, the meeting will be delayed until a room becomes free. The delayed meeting should have the <strong>same</strong> duration as the original meeting.</li>
	<li>When a room becomes unused, meetings that have an earlier original <strong>start</strong> time should be given the room.</li>
</ol>

<p>Return<em> the <strong>number</strong> of the room that held the most meetings. </em>If there are multiple rooms, return<em> the room with the <strong>lowest</strong> number.</em></p>

<p>A <strong>half-closed interval</strong> <code>[a, b)</code> is the interval between <code>a</code> and <code>b</code> <strong>including</strong> <code>a</code> and <strong>not including</strong> <code>b</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 2, meetings = [[0,10],[1,5],[2,7],[3,4]]
<strong>Output:</strong> 0
<strong>Explanation:</strong>
- At time 0, both rooms are not being used. The first meeting starts in room 0.
- At time 1, only room 1 is not being used. The second meeting starts in room 1.
- At time 2, both rooms are being used. The third meeting is delayed.
- At time 3, both rooms are being used. The fourth meeting is delayed.
- At time 5, the meeting in room 1 finishes. The third meeting starts in room 1 for the time period [5,10).
- At time 10, the meetings in both rooms finish. The fourth meeting starts in room 0 for the time period [10,11).
Both rooms 0 and 1 held 2 meetings, so we return 0. 
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 3, meetings = [[1,20],[2,10],[3,5],[4,9],[6,8]]
<strong>Output:</strong> 1
<strong>Explanation:</strong>
- At time 1, all three rooms are not being used. The first meeting starts in room 0.
- At time 2, rooms 1 and 2 are not being used. The second meeting starts in room 1.
- At time 3, only room 2 is not being used. The third meeting starts in room 2.
- At time 4, all three rooms are being used. The fourth meeting is delayed.
- At time 5, the meeting in room 2 finishes. The fourth meeting starts in room 2 for the time period [5,10).
- At time 6, all three rooms are being used. The fifth meeting is delayed.
- At time 10, the meetings in rooms 1 and 2 finish. The fifth meeting starts in room 1 for the time period [10,12).
Room 0 held 1 meeting while rooms 1 and 2 each held 2 meetings, so we return 1. 
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 100</code></li>
	<li><code>1 &lt;= meetings.length &lt;= 10<sup>5</sup></code></li>
	<li><code>meetings[i].length == 2</code></li>
	<li><code>0 &lt;= start<sub>i</sub> &lt; end<sub>i</sub> &lt;= 5 * 10<sup>5</sup></code></li>
	<li>All the values of <code>start<sub>i</sub></code> are <strong>unique</strong>.</li>
</ul>

#define ll long long
struct Meeting{
        int start;
        ll end;
        Meeting(int start,ll end){
            this->start=start;
            this->end=end;
        }
};
struct Room{
    int roomId;
    ll end;
    Room(int roomId, ll end){
        this->roomId=roomId;
        this->end=end;
    }
};
class Compare{
    public:
        bool operator()(Room a,Room b){
            if(a.end==b.end){
                return a.roomId>b.roomId;
            }
            return a.end>b.end;
        }
};
class Solution {
public:
    bool static compare(Meeting a, Meeting b){
        if(a.start==b.start){
            return a.end<b.end;
        }
        return a.start<b.start;
    }
    int mostBooked(int N,vector<vector<int>>& intervals) {
        int n=intervals.size();
        if(n==0)
            return 0;
        vector<Meeting> meetings;
        for(auto i:intervals){
            struct Meeting meeting(i[0],(ll)i[1]);
            meetings.push_back(meeting);
        }
        sort(meetings.begin(),meetings.end(),compare);
        int end=meetings[0].end;
        vector<int> mostUsed(N,0);
        priority_queue<Room,vector<Room>,Compare> pq;
        for(int i=0;i<N;i++){
            pq.push(Room(i,(ll)0));
        }
        for(int i=0;i<n;i++){
            int start=meetings[i].start,end=meetings[i].end;
            set<int> roomsFreed;
            while(!pq.empty() && start>=pq.top().end){
                roomsFreed.insert(pq.top().roomId);
                pq.pop();
            }
            for(auto id:roomsFreed){
                pq.push(Room(id,(ll)0));
            }
            Room room=pq.top();
            if(start<room.end){ //no empty room
                pq.pop();
                int roomId=room.roomId;
                ll endTime=room.end;
                mostUsed[roomId]++;
                pq.push(Room(roomId,endTime+end-start));
            }
            else{
                pq.pop();
                int roomId=room.roomId;
                mostUsed[roomId]++;
                pq.push(Room(roomId,end));
            }
        }
        int mostFreq=0;
        for(auto i:mostUsed){
            mostFreq=max(mostFreq,i);
            //cout<<i<<" ";
        }
        for(int i=0;i<N;i++){
            if(mostUsed[i]==mostFreq)
                return i;
        }
        return 0;
    }
};
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