[LeetCode] Merge Intervals

Thought:
First sort by the start time, then merge.

Code:
public class Solution {
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {

        if (intervals.size() == 0) return intervals;
        Collections.sort(intervals, BYSTART);
        ArrayList<Interval> ret = new ArrayList<Interval>();

        int s = intervals.get(0).start;
        int e = intervals.get(0).end;
        for ( Interval itv : intervals) {
            if (e >= itv.start) e = Math.max(e, itv.end);
            else {
                ret.add(new Interval(s, e));
                s = itv.start;
                e = itv.end;
            }
        }
        ret.add(new Interval(s, e));

        return ret;
    }

    private static final Comparator<Interval> BYSTART = new Comparator<Interval>(){
        public int compare (Interval i, Interval j) {
            return new Integer(i.start).compareTo(new Integer(j.start));
        }
    };
}