A new compact deletion algorithm for double-array structures

A trie is a well known method for various dictionaries, such as spelling check and morphological analysis. A double-array structure is an efficient data structure combining fast access of a matrix form with the compactness of a list form. The drawback of the double-array is that the space efficiency degrades by empty elements produced in key deletion. Morita et al. (2001) presented a key deletion method eliminating empty elements. However, the space efficiency of this method is low for high frequent deletion and deletion takes much time because the cost depends on the number of the empty elements. This paper presents a fast and compact deletion method by using the property of nodes that have no brothers. From simulation results for 100 thousand keys, the present method is about 330 times faster than Morita´s method and keeps the space efficiency ratio at 100%.