public static void merge(ArrayList<Integer> a, ArrayList<Integer> b) {

        int aSize = a.size();
        int bSize = b.size();

        ArrayList<Integer> merged = new ArrayList<>(aSize + bSize);

        int fooPosition, barPosition, mergedPosition;
        fooPosition = barPosition = mergedPosition = 0;

        while (fooPosition < aSize && barPosition < bSize) {
            if (a.get(fooPosition) < b.get(barPosition)) {
                merged.add(mergedPosition++, a.get(fooPosition++));
            } else {
                merged.add(mergedPosition++, b.get(barPosition++));
            }
        }

        while (fooPosition < aSize) {
            merged.add(mergedPosition++, a.get(fooPosition++));
        }

        while (barPosition < bSize) {
            merged.add(mergedPosition++, b.get(barPosition++));
        }

        a.clear();
        a.addAll(merged);
    }