In this paper, we revisit the classic and well-studied longest common subsequence (LCS) problem and study some new variants, first introduced and studied by Rahman and Iliopoulos [Algorithms for Computing Variants of the Longest Common Subsequence Problem, ISAAC 2006]. Here we define a generalization of these variants, the longest parameterized common subsequence (LPCS) problem, and show how to solve it in O(n2 ) and O(n + R log n) time. Furthermore, we show how to compute two variants of LCS, RELAG and RIFIG in O(n + R) time.
Costas S. Iliopoulos, Marcin Kubica, M. Sohel Rahm