leetcode 56 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; }
 * }
 */
class  {
    public List<Interval> merge(List<Interval> intervals) {
        ArrayList<Interval> ans = new ArrayList<Interval>();
        
        if(intervals.size()==0 || intervals == null){
            return ans;
        }
        Collections.sort(intervals, new Comparator<Interval>(){
            
            public int compare(Interval o1, Interval o2){
                    if(o1.start < o2.start){
                    return -1;
                }
                else if(o1.start > o2.start){
                    return 1;
                }
                else{
                    return 0;
                }
            }
        });
        int start = intervals.get(0).start;
        int end = intervals.get(0).end;
        for(int i=1; i< intervals.size(); i++){
            if(intervals.get(i).start <= end && intervals.get(i).end <= end){
                         
            }
            else if(intervals.get(i).start <= end && intervals.get(i).end > end){
                end = intervals.get(i).end;
            }
            else{
                ans.add(new Interval(start, end));
                start = intervals.get(i).start;
                end = intervals.get(i).end;
            }
            
        }
        ans.add(new Interval(start, end));
        return ans;
        
    }
}

class  {
    private class IntervalComparator implements Comparator<Interval> {
        
        public int compare(Interval a, Interval b) {
            return a.start < b.start ? -1 : a.start == b.start ? 0 : 1;
        }
    }

    public List<Interval> merge(List<Interval> intervals) {
        Collections.sort(intervals, new IntervalComparator());

        LinkedList<Interval> merged = new LinkedList<Interval>();
        for (Interval interval : intervals) {
            // if the list of merged intervals is empty or if the current
            // interval does not overlap with the previous, simply append it.
            if (merged.isEmpty() || merged.getLast().end < interval.start) {
                merged.add(interval);
            }
            // otherwise, there is overlap, so we merge the current and previous
            // intervals.
            else {
                merged.getLast().end = Math.max(merged.getLast().end, interval.end);
            }
        }

        return merged;
    }