Lintcode 919. 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

Code (Java):

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/**  * Definition of Interval:  * public classs Interval {  *     int start, end;  *     Interval(int start, int end) {  *         this.start = start;  *         this.end = end;  *     }  * }  */   public class Solution {     /**      * @param intervals: an array of meeting time intervals      * @return: the minimum number of conference rooms required      */     public int minMeetingRooms(List<Interval> intervals) {         if (intervals == null || intervals.size() == 0) {             return 0;         }           List<Event> events = new ArrayList<>();         for (Interval interval : intervals) {             events.add(new Event(interval.start, 0));             events.add(new Event(interval.end, 1));         }           Collections.sort(events, new MyEventComparator());           int ans = 0;         int activeMeetings = 0;           for (Event event : events) {             if (event.flag == 0) {                 activeMeetings++;             } else {                 activeMeetings--;             }               ans = Math.max(ans, activeMeetings);         }           return ans;     } }   class Event {     int time;     int flag; // 0 start, 1 end       public Event(int time, int flag) {         this.time = time;         this.flag = flag;     } }   class MyEventComparator implements Comparator<Event> {     @Override     public int compare(Event a, Event b) {         if (a.time != b.time) {             return a.time - b.time;         }           return b.flag - a.flag;     } }