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/**
 * 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 ) throw new IllegalArgumentException();
        if(intervals.length <= 1) return intervals.length;
        //sort by start
        Arrays.sort(intervals, new Comparator<Interval>(){
            public int compare(Interval l1, Interval l2){
                return l1.start - l2.start;
            } 
        });
        Queue<Interval> pq = new PriorityQueue<>(new Comparator<Interval>(){
             public int compare(Interval l1, Interval l2){
                return l1.end - l2.end;
            } 
        });
        for(int i = 0; i < intervals.length; i ++){
            if(pq.isEmpty()){
                pq.offer(intervals[i]);
            } else {
                Interval cur = pq.peek();
                if(cur.end <= intervals[i].start){
                    pq.poll();
                }
                pq.offer(intervals[i]);
            }
        }
        return pq.size();
    }
}

/**
 * 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 < 1) return 0;
        int len = intervals.length;
        int[] starts = new int[len];
        int[] ends = new int[len];
        
        for (int i = 0; i < len; i++) {
            starts[i] = intervals[i].start;
            ends[i] = intervals[i].end;
        }
        
        Arrays.sort(starts);
        Arrays.sort(ends);
        int res = 0;
        int endIdx = 0;
        for (int i = 0; i < len; i++) {
            if (starts[i] < ends[endIdx]) {
                res++;
            } else {
                endIdx++;
            }
        }
        return res;
    }
}