A Note on the Expected Length of the Longest Common Subsequences of two i.i.d. Random Permutations

  • Christian Houdré
  • Chen Xu
Keywords: Random permutation, Longest common subsequence


We address a question and a conjecture on the expected length of the longest common subsequences of two i.i.d. random permutations of $[n]:=\{1,2,...,n\}$. The question is resolved by showing that the minimal expectation is not attained in the uniform case. The conjecture asserts that $\sqrt{n}$ is a lower bound on this expectation, but we only obtain $\sqrt[3]{n}$ for it.

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