/**
 * 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; }
 * }
 */
class Solution {
    public int minMeetingRooms(Interval[] intervals) {

        Arrays.sort(intervals, new Comparator<Interval>(){
            public int compare(Interval a, Interval b){
                if(a.start == b.start){
                    return a.end - b.end;
                }
                return a.start - b.start;
            }
        });

        ArrayList<ArrayList<Integer>> matrix = new ArrayList<>();
        matrix.add(new ArrayList<Integer>());

        for(Interval inter: intervals){
            boolean insert = false;
            int m = 0;
            while(!insert){
                ArrayList<Integer> currRoom = matrix.get(m);
                int spot = currRoom.size() - 1;
                if(spot == -1){
                    currRoom.add(inter.end);
                    insert = true;
                }
                else if(currRoom.get(spot) <= inter.start){
                    currRoom.add(inter.end);
                    insert = true;
                }
                else{
                    m++;
                    if(m >= matrix.size()){
                        matrix.add(new ArrayList<Integer>());
                    }
                }
            }
        }
        if(matrix.get(0).size() == 0){
            return 0;
        }
        return matrix.size();
    }
}