Consider the sequence alignment problem over a four-letter alphabet {z1, z2, z3, z4}, with a given gap cost and given mismatch costs. Assume that each of these parameters is a positive integer. Suppose you are given two strings A = a1 a2 ... am and B = b1b2 ... bn and a proposed alignment between them. Give an O(mn) algorithm to decide whether this alignment is the unique minimum-cost alignment between A and B