quickSort

private static List<Integer> quickSort(List<Integer> listToSort) {
        if (listToSort.size() <= 1) {
            return listToSort;
        }

        int pivot = listToSort.get(0);

        List<Integer> lesser = listToSort.stream()
                .skip(1)
                .filter(x -> x <= pivot)
                .collect(Collectors.toList());
        List<Integer> greater = listToSort.stream()
                .filter(x -> x > pivot)
                .collect(Collectors.toList());

        lesser = quickSort(lesser);
        lesser.add(pivot);
        greater = quickSort(greater);

        return Stream.concat(lesser.stream(), greater.stream()).collect(Collectors.toList());
    }