Grammar-Compressed Indexes with Logarithmic Search Time

04/01/2020

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by   Francisco Claude, et al.

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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 right-hand sides of the rules). Such a grammar, called a grammar-compressed representation of T, can be encoded using essentially G g bits. We introduce the first grammar-compressed index that uses O(G n) bits and can find the occ occurrences of patterns P[1..m] in time O((m^2+occ) G). We implement the index and demonstrate its practicality in comparison with the state of the art, on highly repetitive text collections.