Explanation:No combination of characters from s1 and s2, while preserving their relative order, can form s3. For example, at index 6, s3 has 'b', but s1[2]='b' and s2[3]='b'. If we take from s1, s3[6]='b' matches s1[2], then we'd need to interleave 'cc' and 'dbbca' to get 'baccc'. This path ultimately fails as the 'a' cannot be accounted for in the correct position.
Example 3:
Input:s1 = "", s2 = "", s3 = ""
Output:true
Explanation:When all strings are empty, s3 is trivially formed by interleaving s1 and s2.