java-multiset-implementation

static class Multiset<E> {
        private NavigableMap<E, Integer> map;
        int totalElements;

        public Multiset() {
            map = new TreeMap<>();
            totalElements = 0;
        }

        public void add(E element) {
            map.put(element, map.getOrDefault(element, 0) + 1);
            totalElements += 1;
        }

        public void remove(E element) {
            int count = map.getOrDefault(element, 0);
            if(count > 0) {
                map.put(element, count - 1);
                count -= 1;
                if(count == 0) {
                    map.remove(element);
                }
                totalElements -= 1;
            }
        }

        public int count(E element) {
            return map.getOrDefault(element, 0);
        }

        public int size() {
            return totalElements;
        }

        public boolean isEmpty() {
            return map.isEmpty();
        }

        public E firstEntry() {
            Map.Entry<E, Integer> entry = map.firstEntry();
            return entry.getKey();
        }

        public E lastEntry() {
            Map.Entry<E, Integer> entry = map.lastEntry();
            return entry.getKey();
        }
    }