We introduce a new family of string processing problems. Given two or more strings, we are asked to compute a factor common to all strings that preserves a specific property and has maximal length. We consider three fundamental string properties: square-free factors, periodic factors, and palindromic factors under three different settings, one per property. In the first setting, we are given a string x and we are asked to construct a data structure over x answering the following type of online queries: given a string y, find a longest square-free factor common to x and y. In the second setting, we are given k strings and an integer 1<k≤k and we are asked to find a longest periodic factor common to at least k strings. In the third one, we are given two strings and we are asked to find a longest palindromic factor common to the two strings. We present linear-time solutions for all settings. This is a full and extended version of a paper from SPIRE 2018.

Original languageEnglish
Pages (from-to)244-251
Number of pages8
JournalTheoretical Computer Science
Publication statusPublished - 6 Apr 2020


  • Palindromic factors
  • Periodic factors
  • Square-free factors


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