Longest common extensions in sublinear space

Abstract

The longest common extension problem (LCE problem) is to construct a data structure for an input string T of length n that supports LCE(i, j) queries. Such a query returns the length of the longest common prefix of the suffixes starting at positions i and j in T. This classic problem has a well-known solution that uses (n) space and O(1) query time. In this paper we show that for any trade-off parameter 1 ≤ τ ≤ n, the problem can be solved in O(image found) space and O(τ) query time. This significantly improves the previously best known time-space trade-offs, and almost matches the best known time-space product lower bound.