Given a collection of intervals, merge all overlapping intervals.

MergeIntervals.java

// [1,3],[2,6],[8,10],[15,18] -> [1,6],[8,10],[15,18]
public List<Interval> merge(List<Interval> intervals) {
    Collections.sort(intervals, (i1, i2) -> i1.start - i2.start);

    List<Interval> mergedIntervals = new ArrayList<>();

    for(int i = 0; i < intervals.size(); i++) {
        int start = intervals.get(i).start;
        int end = intervals.get(i).end;

        while(i+1 < intervals.size() && intervals.get(i+1).start <= end) {
            end = Math.max(end, intervals.get(++i).end);
        }

        mergedIntervals.add(new Interval(start, end));
    }

    return mergedIntervals;
}