ceiling() with TreeMultimap

Question

• Is it possible to extend TreeMultimap from Google's guava to get some king odd ceiling function? ceiling(key) would return the smallest key greater than the given one. (I know I could get an ordered set view and just look, but I would prefer something with beter time complexity, like a balanced binary search tree offers)
• Is there any other library that would implement a balanced binary search tree and allow that?
• What is the complexity of common operations of TreeMultimap?

Answer 1

multimap.keySet().ceiling(key)

does it pretty directly, but you need Java 6 and the most recent Guava release, 14.0, which is when TreeMultimap.keySet() started returning NavigableSet . The complexity is O(log #keys), exactly as you would expect.

Answer 2

K ceiling(K key, TreeMultimap<K,V> map) {
  SortedSet<K> keyset = map.keySet();
  SortedSet<K> head = keyset.headSet(key);
  return headSet.isEmpty() ? null : head.last();    
}

The documentation doesn't mention any time guarantees for the operations, but I would expect it to run in logarithmic time since both keySet and headSet appear to return views of the underlying data rather than building new collections themselves.