/**
 * 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>& intervals) {
        int n = intervals.size();
        if(!n)return 0;
        sort(intervals.begin(), intervals.end(), [](const Interval& i1, const Interval& i2){ return i1.start < i2.start; });
        int depth = 1;
        priority_queue<int, vector<int>, greater<int>> ends;
        ends.push(intervals[0].end);
        for(int i = 1; i < intervals.size(); ++i)
        {
            auto interval = intervals[i];
            while(ends.size() && interval.start >= ends.top())
                ends.pop();
            ends.push(interval.end);
            depth = max(depth, static_cast<int>(ends.size()));
        }
        return depth;
    }
};