253. Meeting Rooms II

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
public class Solution {
    public int minMeetingRooms(Interval[] intervals) {
        if(intervals==null||intervals.length==0) return 0;
        Arrays.sort(intervals,(a,b)->(a.start-b.start));
        int max=0;
        PriorityQueue<Interval> queue=new PriorityQueue<>(intervals.length,(a,b)->(a.end-b.end));
        for(int i=0;i<intervals.length;i++){
            while(!queue.isEmpty()&&intervals[i].start>=queue.peek().end) queue.poll();
            queue.offer(intervals[i]);
            max=Math.max(max,queue.size());
        }
        return max;
    }
}

public class Solution {
    public int minMeetingRooms(Interval[] intervals) {
        int[] starts = new int[intervals.length];
        int[] ends = new int[intervals.length];
        for(int i=0; i<intervals.length; i++) {
            starts[i] = intervals[i].start;
            ends[i] = intervals[i].end;
        }
        Arrays.sort(starts);
        Arrays.sort(ends);
        int rooms = 0;
        int endsItr = 0;
        for(int i=0; i<starts.length; i++) {
            if(starts[i]<ends[endsItr])
                rooms++;
            else
                endsItr++;
        }
        return rooms;
    }
}