Abstract

Let a text T[1..n] be the only string generated by a context-free grammar with g (terminal and nonterminal) symbols, and of size G (measured as the sum of the lengths of the righthand sides of the rules). Such a grammar, called a grammar-compressed representation of T, can be encoded using G lg G bits. We introduce the first grammar-compressed index that uses O(G lg n) bits (precisely, G lg n + (2 + E)G lg g for any constant epsilon > 0) and can find the occ occurrences of patterns P[1..m] in time O ((m(2) + occ) lg G). We implement the index and demonstrate its practicality in comparison with the state of the art, on highly repetitive text collections. (c) 2020 Elsevier Inc. All rights reserved.