merge intervals

 * 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; }
 * }
 */
public class  {
    public List<Interval> merge(List<Interval> intervals) {
        if(intervals.size()<=1) return intervals;
        intervals.sort((o1,o2)->Integer.compare(o1.start,o2.start));
        int start = intervals.get(0).start;
        int end = intervals.get(0).end;
        List<Interval> res = new ArrayList<Interval>();
        for(int i=0; i<intervals.size();i++) {
            if(intervals.get(i).start <= end) {
                end = Math.max(end,intervals.get(i).end);
            } else {
                res.add(new Interval(start,end));
                start = intervals.get(i).start;
                end = intervals.get(i).end;
            }
        }
        res.add(new Interval(start,end)); 
        return res;
    }
}