有类似的题在Acw，但是一时间找不到了，这个做法也可以理解
MD的十点半了，又是20分钟

class Solution {
public:
// 看题解
// https://leetcode.cn/problems/meeting-rooms-ii/solution/labuladong-sao-miao-xian-ji-qiao-an-pai-h0f5d/
    int minMeetingRooms(vector<vector<int>>& meetings) {
        int n = meetings.size();
        vector<int> begin(n);
        vector<int> end(n);
        for (int i = 0; i < n; i ++ ) {
            begin[i] = meetings[i][0];
            end[i] = meetings[i][1];
        }

        sort(begin.begin(), begin.end());
        sort(end.begin(), end.end());

        int l = 0, r = 0;
        int cnt = 0, res = 0;
        while (l < n && r < n) {
            if (begin[l] < end[r]) {
                cnt ++ ;
                l ++ ;
            }
            else {
                cnt -- ;
                r ++ ;
            }
            res = max(res, cnt);
        }

        return res;
    }
};