Give an algorithm to take in a set of k strings and to find the longest common substring of each of the k 2 pairs of strings. Assume each string is of length n. Since the longest common substring of any pair can be found in O(n) time, O(k 2n) time clearly suffices. Now suppose that the string lengths are different but sum to M. Show how to find all the longest common substrings in time O(kM).