4. We can consider LCS(X,Y) as a matching between some character of X to some char- acters in Y. For example LCS(" AAB" AB") contains two matchings, both of length 2. See Figure 1 X = "AD A B" X = AD AB" * p *** Y = "AB Y = "AB Figure 1: Two different matchings. Both of them are solutions to LCS(ADAB", "AB") Suggest an algorithm, as efficient as possible, that receives two sequences X and Y, and return 'YES' if and only if there are two different matchings, both are solutions to LCS(X,Y)