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.

MinMeetingRooms.java

public int minMeetingRooms(Interval[] intervals) {
    if(intervals == null || intervals.length == 0)
        return 0;

    Arrays.sort(intervals, (i1, i2) -> i1.start - i2.start);
    PriorityQueue<Interval> queue = new PriorityQueue<>(intervals.length, (i1, i2) -> i1.end-i2.end);  

    queue.offer(intervals[0]);                  // start with a room 

    for(int i = 1; i < intervals.length; i++) {
        Interval interval = queue.poll();       // get interval that ends the soonest

        if(intervals[i].start >= interval.end) // if no overlap, change the end time of the room 
            interval.end = intervals[i].end;
        else
            queue.offer(intervals[i]);        // if overlap, add room 

        queue.offer(interval);               // put room back in priority queue
    }

    return queue.size();                    // each element in queue represents a room 
}