public static int equalStacks(List<Integer> h1, List<Integer> h2, List<Integer> h3) {
    // Write your code here
        // there are 3 stacks involved
        List<Integer> cumulHeights = new ArrayList<>();
        Integer cumul = 0;
        for (int i = h1.size() - 1; i>=0; i--) {
            cumul += h1.get(i);
            cumulHeights.add(cumul);
        }
        cumul = 0;
        for (int i = h2.size() - 1; i>=0; i--) {
            cumul += h2.get(i);
            cumulHeights.add(cumul);
        }
        cumul = 0;
        for (int i = h3.size() - 1; i>=0; i--) {
            cumul += h3.get(i);
            cumulHeights.add(cumul);
        }
        Optional<Map.Entry<Integer, Long>> mm = cumulHeights.stream().collect(Collectors.groupingBy(s -> s, Collectors.counting())).entrySet()
                .stream().filter((s) -> s.getValue() == 3).max(Comparator.comparingInt(s -> s.getKey()));
        if (mm.isPresent()) {
            return mm.get().getKey();
        }
        return 0;
    }