[Leetcode] Merge Intevals

public class Solution {
    class IntervalAsc implements Comparator<Interval>
      {
        public int compare (Interval o1, Interval o2)
        {
         if (o1.start != o2.start)
            return o1.start < o2.start ? -1 : 1;
          else if (o1.end != o2.end)
            return o1.end < o2.end ? -1 : 1;
          else
            return 0;
      }}

      public ArrayList<Interval> merge (ArrayList<Interval> intervals)
      {
        Collections.sort(intervals, new IntervalAsc());
        ArrayList<Interval> ret = new ArrayList<Interval>();
        int n = intervals.size();
        if(n==0) return ret;
        Interval last=intervals.get(0);
        for(int i=1;i<n;i++){
            if(intervals.get(i).start>last.end){
                ret.add(new Interval(last.start,last.end));
                last=intervals.get(i);
            }else{
                last.end=Math.max(intervals.get(i).end, last.end);
            }
        }
        ret.add(last);
        return ret;
      }

    }