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We describe a compression-aware method to compute all-vs-all maximal exact matches (MEM) among strings of a repetitive collection $\mathcal{T}$. The key concept in our work is the construction of a fully-balanced grammar $\mathcal{G}$ from…

Information Retrieval · Computer Science 2023-06-30 Diego Diaz-Dominguez , Leena Salmela

Computing the {\em matching statistics} of a string $P[1..m]$ with respect to a text $T[1..n]$ is a fundamental problem which has application to genome sequence comparison. In this paper, we study the problem of computing the matching…

Data Structures and Algorithms · Computer Science 2022-01-14 Younan Gao

We introduce a data structure for counting pattern occurrences in texts compressed with any run-length context-free grammar. Our structure uses space proportional to the grammar size and counts the occurrences of a pattern of length $m$ in…

Data Structures and Algorithms · Computer Science 2025-01-30 Gonzalo Navarro , Alejandro Pacheco

Finding maximal exact matches (MEMs) between strings is an important task in bioinformatics, but it is becoming increasingly challenging as geneticists switch to pangenomic references. Fortunately, we are usually interested only in the…

Data Structures and Algorithms · Computer Science 2024-07-02 Travis Gagie

Two recent lower bounds on the compressibility of repetitive sequences, $\delta \le \gamma$, have received much attention. It has been shown that a length-$n$ string $S$ over an alphabet of size $\sigma$ can be represented within the…

Data Structures and Algorithms · Computer Science 2023-11-10 Tomasz Kociumaka , Gonzalo Navarro , Francisco Olivares

In this paper, we describe a new type of match between a pattern and a text that aren't necessarily maximal in the query, but still contain useful matching information: locally maximal exact matches (LEMs). There are usually a large amount…

Data Structures and Algorithms · Computer Science 2025-05-22 Ahsan Sanaullah , Degui Zhi , Shaojie Zhang

We describe the first self-indexes able to count and locate pattern occurrences in optimal time within a space bounded by the size of the most popular dictionary compressors. To achieve this result we combine several recent findings,…

Data Structures and Algorithms · Computer Science 2019-09-06 Anders Roy Christiansen , Mikko Berggren Ettienne , Tomasz Kociumaka , Gonzalo Navarro , Nicola Prezza

Given a pattern string $P$ of length $n$ and a query string $T$ of length $m$, where the characters of $P$ and $T$ are drawn from an alphabet of size $\Delta$, the {\em exact string matching} problem consists of finding all occurrences of…

Data Structures and Algorithms · Computer Science 2015-10-01 Srikrishnan Divakaran

In this paper we revisit the classical regular expression matching problem, namely, given a regular expression $R$ and a string $Q$, decide if $Q$ matches one of the strings specified by $R$. Let $m$ and $n$ be the length of $R$ and $Q$,…

Data Structures and Algorithms · Computer Science 2007-05-23 Philip Bille

Given a set of pattern strings $\mathcal{P}=\{P_1, P_2,\ldots P_k\}$ and a text string $S$, the classic dictionary matching problem is to report all occurrences of each pattern in $S$. We study the dictionary problem in the compressed…

Data Structures and Algorithms · Computer Science 2025-09-04 Philip Bille , Inge Li Gørtz , Simon J. Puglisi , Simon R. Tarnow

We study the problem of finding maximal exact matches (MEMs) between a query string $Q$ and a labeled graph $G$. MEMs are an important class of seeds, often used in seed-chain-extend type of practical alignment methods because of their…

Data Structures and Algorithms · Computer Science 2023-07-04 Nicola Rizzo , Manuel Cáceres , Veli Mäkinen

We consider document listing on string collections, that is, finding in which strings a given pattern appears. In particular, we focus on repetitive collections: a collection of size $N$ over alphabet $[1,\sigma]$ is composed of $D$ copies…

Data Structures and Algorithms · Computer Science 2018-11-15 Gonzalo Navarro

The most fundamental problem considered in algorithms for text processing is pattern matching: given a pattern $p$ of length $m$ and a text $t$ of length $n$, does $p$ occur in $t$? Multiple versions of this basic question have been…

Data Structures and Algorithms · Computer Science 2021-11-10 Moses Ganardi , Paweł Gawrychowski

Given a pattern string $P$ of length $n$ consisting of $\delta$ distinct characters and a query string $T$ of length $m$, where the characters of $P$ and $T$ are drawn from an alphabet $\Sigma$ of size $\Delta$, the {\em exact string…

Data Structures and Algorithms · Computer Science 2015-12-14 Srikrishnan Divakaran

Pattern matching is a fundamental process in almost every scientific domain. The problem involves finding the positions of a given pattern (usually of short length) in a reference stream of data (usually of large length). The matching can…

Data Structures and Algorithms · Computer Science 2022-07-01 Anas Al-okaily , Abdelghani Tbakhi

Given strings $P$ of length $m$ and $T$ of length $n$ over an alphabet of size $\sigma$, the string matching with $k$-mismatches problem is to find the positions of all the substrings in $T$ that are at Hamming distance at most $k$ from…

Data Structures and Algorithms · Computer Science 2013-08-01 Emanuele Giaquinta , Szymon Grabowski , Kimmo Fredriksson

A Random Access query to a string $T\in [0..\sigma)^n$ asks for the character $T[i]$ at a given position $i\in [0..n)$. In $O(n\log\sigma)$ bits of space, this fundamental task admits constant-time queries. While this is optimal in the…

Data Structures and Algorithms · Computer Science 2026-05-13 Anouk Duyster , Tomasz Kociumaka

In this paper we are interested in indexing texts for substring matching queries with one edit error. That is, given a text $T$ of $n$ characters over an alphabet of size $\sigma$, we are asked to build a data structure that answers the…

Data Structures and Algorithms · Computer Science 2014-08-25 Djamal Belazzougui

We describe an algorithm to find maximal exact matches (MEMs) among HiFi reads with homopolymer errors. The main novelty in our work is that we resort to run-length compression to help deal with errors. Our method receives as input a…

Data Structures and Algorithms · Computer Science 2022-09-01 Diego Díaz-Domínguez , Simon J. Puglisi , Leena Salmela

Unlike in statistical compression, where Shannon's entropy is a definitive lower bound, no such clear measure exists for the compressibility of repetitive sequences. Since statistical entropy does not capture repetitiveness, ad-hoc measures…

Data Structures and Algorithms · Computer Science 2021-01-18 Tomasz Kociumaka , Gonzalo Navarro , Nicola Prezza
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