56. Merge Interval

class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        List<Interval> res = new ArrayList<>();
        if (intervals == null || intervals.size() == 0) return res;

        intervals.sort((i1, i2) -> Integer.compare(i1.start, i2.start));

        int start = intervals.get(0).start;
        int end = intervals.get(0).end;

        for (Interval interval : intervals) {
            // Overlapped
            if (interval.start <= end) {
                end = Math.max(interval.end, end);
            } else {
                res.add(new Interval(start, end));
                start = interval.start;
                end = interval.end;
            }
        }

        res.add(new Interval(start, end));

        return res;
    }
}