leetcode-253：会议室 II

输入：intervals = [[0,30],[5,10],[15,20]]
输出：2

输入：intervals = [[7,10],[2,4]]
输出：1

class Solution {
public:
    int minMeetingRooms(vector<vector<int>>& intervals) {
        if(intervals.size()==0) return 0;
        vector<pair<int,int>> meetings;
        for(auto it:intervals){
            meetings.push_back({it[0],1});
            meetings.push_back({it[1],-1});
        }
        sort(meetings.begin(),meetings.end());
        int res=0;
        int count=0;
        for(auto& it:meetings){
            count+=it.second;
            res=max(res,count);
        }
        return res;
    }
};