Dynamic index and LZ factorization in compressed space

TL;DR

This paper introduces a new dynamic compressed index with efficient search and update capabilities, based on signature encoding and LZ77 factorization, significantly reducing space and time complexity for text operations.

Contribution

It presents a novel dynamic compressed index of size O(w) that supports efficient pattern search and substring updates, along with a space-efficient LZ77 factorization algorithm.

Findings

Supports pattern search in O(|P| f_A + ... + occ log N) time

Enables substring insertion/deletion in polylogarithmic time

Provides a space-efficient LZ77 factorization algorithm with improved runtime

Abstract

In this paper, we propose a new \emph{dynamic compressed index} of $O(w)$ space for a dynamic text $T$, where $w = O(\min(z \log N \log^*M, N))$ is the size of the signature encoding of $T$, $z$ is the size of the Lempel-Ziv77 (LZ77) factorization of $T$, $N$ is the length of $T$, and $M \geq 3N$ is an integer that can be handled in constant time under word RAM model. Our index supports searching for a pattern $P$ in $T$ in $O(|P| f_{\mathcal{A}} + \log w \log |P| \log^* M (\log N + \log |P| \log^* M) + \mathit{occ} \log N)$ time and insertion/deletion of a substring of length $y$ in $O((y+ \log N\log^* M)\log w \log N \log^* M)$ time, where $f_{\mathcal{A}} = O(\min \{ \frac{\log\log M \log\log w}{\log\log\log M}, \sqrt{\frac{\log w}{\log\log w}} \})$. Also, we propose a new space-efficient LZ77 factorization algorithm for a given text of length $N$, which runs in $O(N f_{\mathcal{A}} + z \log w \log^3 N (\log^* N)^2)$ time with $O(w)$ working space.