Microsoft Developer interview questions

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: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b.