ABABAABA

You are given a uniformly randomly generated string S, consisting of letters from the set {"A", "B"}. Your task is to find a string T that appears in S as a subsequence exactly twice. In other words, you need to find such a string T, that there exist exactly two sets of indexes i1, i2, ..., i|T| and j1, j2, ..., j|T| such that there exists some k, where ik ≠ jk and S{i1...i|T|} = S{j1...j|T|} =