Oracle phone

freelist.java

ArrayList<Interval> getFreeList(long start, long end, ArrayList<ArrayList<Interval>> busyLists) {
        ArrayList<Interval> result = new ArrayList<>();
        if (start >= end) return result;

        if (busyLists.size() == 0) {
            result.add(new Interval(start, end));
            return result;
        }

        ArrayList<Interval> globalList = new ArrayList<>();
        for (ArrayList<Interval> list : busyLists) globalList.addAll(list);
        if (globalList.size() == 0) {
            result.add(new Interval(start, end));
            return result;
        }

        Collections.sort(globalList, new IntervalComparator());

        long latestSoFar = start;

        for (int i = 0; i < globalList.size(); ++i) {
            if (latestSoFar >= end) return result;

            Interval current = globalList.get(i);
            if (current.start >= end) return result;

            if (current.start > latestSoFar) {
                result.add(new Interval(latestSoFar, Math.min(current.start, end)));
            }

            latestSoFar = Math.max(latestSoFar, current.end);

        }

        if (latestSoFar < end) result.add(new Interval(latestSoFar, end));

        return result;
}

class IntervalComparator implements Comparator<Interval> {
    @Override
    public int compare(Interval i1, Interval i2) {
        return i1.start == i2.start ? Long.compare(i1.end, i2.end) : Long.compare(i1.start, i2.start);

    }
}