public int size() {
if (from == null && to == null) return root.size;
if (from == null) {
Node to = toInclusive ? root.floor(this.to) : root.lower(this.to);
if (to == nullNode) return 0;
return root.indexOf(to) + 1;
}
if (to == null) {
Node from = fromInclusive ? root.ceil(this.from) : root.higher(this.from);
if (from == nullNode) return 0;
return root.size - root.indexOf(from);
}
Node from = fromInclusive ? root.ceil(this.from) : root.higher(this.from);
if (from == nullNode || !belongs(from.key)) return 0;
Node to = toInclusive ? root.floor(this.to) : root.lower(this.to);
return root.indexOf(to) - root.indexOf(from) + 1;
}
public K lower(K k) {
Node target = root.lower(k);
if (target == nullNode) return null;
if (belongs(target.key)) return target.key;
return null;
}
protected Node lower(K key) {
if (compare(key, this.key) <= 0) return left.lower(key);
Node result = right.lower(key);
if (result == nullNode) return this;
return result;
}