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.

• Time: O(n)
• Space: O(1)

public int minMeetingRooms(Interval[] intervals) {
    if (intervals.length <= 1) {
        return intervals.length;
    }
    Arrays.sort(intervals,(a, b) -> a.start - b.start);
    PriorityQueue<Interval> pq = new PriorityQueue<>((a, b) -> a.end - b.end);
    pq.offer(intervals[0]);
    for (int i = 1; i < intervals.length; i++) {
        Interval pre = pq.poll();
        if (pre.end <= intervals[i].start) {
            pre.end = intervals[i].end;
        } else {
            pq.offer(intervals[i]);
        }
        pq.offer(pre);
    }
    return pq.size();
}