LeetCode Q253: Meeting Rooms II

Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required.

For example,
Given [[0, 30],[5, 10],[15, 20]],
return 2.

Solution:

	/**
	* Definition for an interval.
	* struct Interval {
	* int start;
	* int end;
	* Interval() : start(0), end(0) {}
	* Interval(int s, int e) : start(s), end(e) {}
	* };
	*/
	class Solution {
	public:
	bool static compare(Interval a, Interval b){
	return a.start<b.start;
	}
	int minMeetingRooms(vector<Interval>& intervals) {
	if(intervals.size()==0)
	return 0;
	sort(intervals.begin(), intervals.end(), compare);
	vector<vector<Interval> > classRoom;
	auto cmp = [](pair<int, int> a, pair<int, int> b) {return a.first > b.first;};
	priority_queue<pair<int, int>, std::vector<pair<int, int> >, decltype(cmp)> mypq(cmp);
	for(int i=0; i<intervals.size(); i++){
	Interval itv = intervals[i];
	if(mypq.empty()){
	vector<Interval> newRoom;
	newRoom.push_back(itv);
	mypq.push(pair<int, int> (itv.end, newRoom.size()-1));
	classRoom.push_back(newRoom);
	continue;
	}
	pair<int, int> top = mypq.top();
	if(itv.start >= top.first){
	classRoom[top.second].push_back(itv);
	mypq.pop();
	mypq.push(pair<int, int> (itv.end, top.second));
	}else{
	vector<Interval> newRoom;
	newRoom.push_back(itv);
	mypq.push(pair<int, int> (itv.end, newRoom.size()-1));
	classRoom.push_back(newRoom);
	}
	}
	return classRoom.size();
	}
	};

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Round 2 solution:

	/**
	* Definition for an interval.
	* struct Interval {
	* int start;
	* int end;
	* Interval() : start(0), end(0) {}
	* Interval(int s, int e) : start(s), end(e) {}
	* };
	*/
	class Solution {
	public:
	int minMeetingRooms(vector<Interval>& itvs) {
	int res = 0;
	if(itvs.empty())
	return res;
	sort(itvs.begin(), itvs.end(), [](Interval a, Interval b){return a.start<b.start;});
	priority_queue<int> myPQ;
	for(int i=0; i<itvs.size(); i++){
	Interval itv = itvs[i];
	if(myPQ.empty()){
	myPQ.push(itv.end*-1);
	res++;
	}else{
	int early = myPQ.top()*-1;
	if(early<=itv.start){
	myPQ.pop();
	myPQ.push(itv.end*-1);
	}else{
	res++;
	myPQ.push(itv.end*-1);
	}
	}
	}
	return res;
	}
	};

view raw Q253Rnd2.cpp hosted with ❤ by GitHub