 
Summary: PREPRINT. Information Processing Letters, 46:295300, 1993.
Improved Behaviour of Tries
by Adaptive Branching \Lambda
Arne Andersson Stefan Nilsson
Department of Computer Science, Lund University,
Box 118, S221 00 Lund, Sweden
Abstract
We introduce and analyze a method to reduce the search cost in tries. Tradi
tional trie structures use branching factors at the nodes that are either fixed
or a function of the number of elements. Instead, we let the distribution of
the elements guide the choice of branching factors. This is accomplished in
a strikingly simple way: in a binary trie, the i highest complete levels are
replaced by a single node of degree 2 i ; the compression is repeated in the sub
tries. This structure, the levelcompressed trie, inherits the good properties of
binary tries with respect to neighbour and range searches, while the external
path length is significantly decreased. It also has the advantage of being easy
to implement. Our analysis shows that the expected depth of a stored element
is \Theta(log \Lambda n) for uniformly distributed data.
Keywords: Algorithms, data structures, trie, digital search tree, levelcompressed
trie
