Compacting a Dynamic Edit Distance Table by RLE Compression

Abstract

Kim and Park [A dynamic edit distance table, J. Disc. Algo., 2:302–312, 2004] proposed a method (KP) based on a “dynamic edit distance table” that allows one to efficiently maintain edit distance information between two strings A of length m and B of length n when the strings can be modified by single-character edits to their left or right ends. This type of computation is useful e.g. in cyclic string comparison. KP uses linear time, $O(m+n)$, to update the distance representation after each single edit. As noted in a recent extension of KP by Hyyrö et al. [Incremental string comparison, J. Disc. Algo., 34:2-17, 2015], a practical bottleneck is that the method needs $\varTheta (mn)$ space to store a representation of a complete $m \times n$ edit distance table. In this paper we take the first steps towards reducing the space usage by RLE compressing A and B. Let M and N be the lengths of RLE compressed versions of A and B, respectively. We propose how to store the edit distance table using $\varTheta (mN + Mn)$ space while maintaining the same time complexity as the original method that does not use compression.