// analogous to OptimizedMultiSet

static class MultiSetMapWithTopTen<A, B> extends MultiSetMap<A, B> {

  // outer tree map for sorting

  // inner linked hash set for reproducability (HashSet ordering sucks)

  MultiSetMap<Int, A> byCount = multiSetMap_innerLinkedHashSet_outerRevTreeMap();

  *() {}

  *(bool useTreeMap) { super(useTreeMap); }

  *(MultiSetMap<A, B> map) { super(map); }

  *(Map<A, Set<B>> data) { super(data); }

  private void unindex(A key, Set<B> values) {

    if (nempty(values)) byCount.remove(l(values), key);

  }

  private void index(A key, Set<B> values) {

    if (nempty(values)) byCount.add(l(values), key);

  }

  bool put(A key, B value) { synchronized(data) {

    Set<B> set = data.get(key);

    unindex(key, set);

    if (set == null)

      data.put(key, set = _makeEmptySet());

    bool changed = set.add(value);

    index(key, set);

    if (!changed) false;

    ret true with ++size;

  }}

  void remove(A key) { synchronized(data) {

    Set<B> set = data.get(key);

    if (set == null) ret;

    size -= l(set);

    unindex(key, set);

    data.remove(key);

  }}

  void remove(A key, B value) { synchronized(data) {

    Set<B> set = data.get(key);

    if (set == null) ret;

    unindex(key, set);

    bool changed = set.remove(value);

    index(key, set);

    if (changed) {

      --size;

      if (set.isEmpty())

        data.remove(key);

    }

  }}

  void clear() { synchronized(data) {

    data.clear();

    byCount.clear();

    size = 0;

  }}

  // keys are the values in the byCount multimap

  ItIt<A> keysByPopularityIterator() {

    ret multiSetMapValuesIterator(byCount);

  }

}