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.

Example

Example1

Input: intervals = [(0,30),(5,10),(15,20)]
Output: 2
Explanation:
We need two meeting rooms
room1: (0,30)
room2: (5,10),(15,20)

Example2

Input: intervals = [(2,7)]
Output: 1
Explanation: 
Only need one meeting room

/**
 * Definition of Interval:
 * public classs Interval {
 *     int start, end;
 *     Interval(int start, int end) {
 *         this.start = start;
 *         this.end = end;
 *     }
 * }
 */

public class Solution {
    public int minMeetingRooms(List<Interval> intervals) {
        if (intervals == null || intervals.size() == 0)
            return 0;
        // Sorting in ascending order of start time
        Collections.sort(intervals, (a, b) -> a.start - b.start);
        // Using a Min PQ
        PriorityQueue<Integer> queue = new PriorityQueue<>();
        int count = 1;
        queue.add(intervals.get(0).end);
        for (int i = 1; i < intervals.size(); i++) {
            // If an overlap happens even with the smallest end interval we have
            if (intervals.get(i).start < queue.peek())
                count++;
            else
                queue.poll();
            queue.add(intervals.get(i).end);
        }
        return count;
    }
}