LeetCode: Merge Intervals

Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

For example,
Given [1,3],[2,6],[8,10],[15,18],
return [1,6],[8,10],[15,18].

/**
 * 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; }
 * }
 */

import java.util.Collections;

public class Solution {
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        // Start typing your Java solution below
        // DO NOT write main() function
        Collections.sort(intervals, new Comparator<Interval>(){public int compare(Interval a, Interval b){return a.start>b.start?1:(a.start==b.start?0:-1);}});
        
        ArrayList<Interval> res = new ArrayList<Interval>();
        
        int i=0;
        while(i<intervals.size()){
            int j=i+1;
            int end = intervals.get(i).end;
            while(j<intervals.size() && end>=intervals.get(j).start){
                end=Math.max(end, intervals.get(j).end);
                j++;
            }                
            res.add(new Interval(intervals.get(i).start,end));
            i=j;
           
        }
        return res;
    }
}