meeting_rooms.java

public int minMeetingRooms(Interval[] intervals) {
    HashMap<Integer, Integer> map = new HashMap<>();
    int min=0;
    int max=0;
    for(int i=0;i<intervals.length;i++){
        if(!map.containsKey(intervals[i].start)){
            map.put(intervals[i].start,0);
        }
        if(!map.containsKey(intervals[i].end)){
            map.put(intervals[i].end,0);
        }
        min = Math.min(min, intervals[i].start);
        max = Math.max(max, intervals[i].end);
        map.put(intervals[i].start, map.get(intervals[i].start)+1);
        map.put(intervals[i].end, map.get(intervals[i].end)-1);
    }
    int answer = 0;
    int count=0;
    for(int i=min;i<=max;i++){
        if(map.containsKey(i)){
            count+=map.get(i);
            answer = Math.max(answer ,count);
        }
    }
    return answer;
}