merge/insert interval

public List<Interval> (List<Interval> intervals) {
    if (intervals == null || intervals.size() <= 1)
        return intervals;
    List<Interval> ans = new ArrayList<Interval>();
    Collections.sort(intervals, new Comparator<Interval>(){
        public int compare(Interval i1, Interval i2) {
            return i1.start - i2.start;
        }
    });
    int start = intervals.get(0).start;
    int end = intervals.get(0).end;
    for (Interval it : intervals) {
        if (it.start <= end) {
            
            end = Math.max(end, it.end);
        } else {
            ans.add(new Interval(start, end));
            start = it.start;
            end = it.end;
        }
    }
    ans.add(new Interval(start, end));
    return ans;
}

public List<Interval> insert(List<Interval> intervals, Interval newInterval) {
    intervals.add(newInterval);
    if (intervals.size() == 1)
        return intervals;
    List<Interval> ans = new ArrayList<Interval>();
    Collections.sort(intervals, new Comparator<Interval>(){
        public int compare(Interval i1, Interval i2) {
            return i1.start - i2.start;
        }
    });
    int start = intervals.get(0).start;
    int end = intervals.get(0).end;
    for (Interval it : intervals) {
        if (it.start <= end) {
            
            end = Math.max(end, it.end);
        } else {
            ans.add(new Interval(start, end));
            start = it.start;
            end = it.end;
        }
    }
    ans.add(new Interval(start, end));
    return ans;
}