Restructuring Compressed Texts without Explicit Decompression

TL;DR

This paper introduces algorithms that convert between different compressed text formats directly, without decompression, achieving polynomial time complexity and outperforming traditional methods in worst-case scenarios.

Contribution

It presents the first polynomial-time algorithms for restructuring compressed texts between various formats without explicit decompression, improving efficiency over decompression-based methods.

Findings

Algorithms work directly on compressed data

Conversion times are polynomial in input and output sizes

Outperforms decompression-based conversions in worst-case scenarios

Abstract

We consider the problem of {\em restructuring} compressed texts without explicit decompression. We present algorithms which allow conversions from compressed representations of a string $T$ produced by any grammar-based compression algorithm, to representations produced by several specific compression algorithms including LZ77, LZ78, run length encoding, and some grammar based compression algorithms. These are the first algorithms that achieve running times polynomial in the size of the compressed input and output representations of $T$. Since most of the representations we consider can achieve exponential compression, our algorithms are theoretically faster in the worst case, than any algorithm which first decompresses the string for the conversion.