87. Interleaving String

Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively, such that the substrings are concatenated in an alternating fashion to form the interleaving. The two strings s and t are said to be interleaving if the resulting string preserves the relative order of the characters within each of the strings.