Determine if s3 is formed by interleaving s1 and s2.
An interleaving preserves the order of characters from both strings but allows mixing.
With s1 = "aabcc", s2 = "dbbca", s3 = "aadbbcbcac":
- Take "aa" from s1, "dbbc" from s2, "bc" from s1, "a" from s2, "c" from s1.
- Order preserved in both. Valid interleaving. Return true.
With s1 = "aabcc", s2 = "dbbca", s3 = "aadbbbaccc":
- No valid interleaving produces this s3.
- Return false.
Constraints: s1.length, s2.length .