English

Linear-space LCS enumeration with quadratic-time delay for two strings

Data Structures and Algorithms 2025-05-23 v2

Abstract

Suppose we want to seek the longest common subsequences (LCSs) of two strings as informative patterns that explain the relationship between the strings. The dynamic programming algorithm gives us a table from which all LCSs can be extracted by traceback. However, the need for quadratic space to hold this table can be an obstacle when dealing with long strings. A question that naturally arises in this situation would be whether it is possible to exhaustively search for all LCSs one by one in a time-efficient manner using only a space linear in the LCS length, where we treat read-only memory for storing the strings as excluded from the space consumed. As a part of the answer to this question, we propose an O(L)O(L)-space algorithm that outputs all distinct LCSs of the strings one by one each in O(n2)O(n^2) time, where the strings are both of length nn and LL is the LCS length of the strings.

Keywords

Cite

@article{arxiv.2504.05742,
  title  = {Linear-space LCS enumeration with quadratic-time delay for two strings},
  author = {Yoshifumi Sakai},
  journal= {arXiv preprint arXiv:2504.05742},
  year   = {2025}
}

Comments

10 pages

R2 v1 2026-06-28T22:50:27.129Z