A classmate came up with a problem and challenged me to solve it, but he is not sure if this problem is even solvable or not, and I haven't figure out a solution.

Given 2 strings $$$A$$$ and $$$B$$$, count how many $$$DIFFERENT$$$ strings that can be created by combining a prefix of $$$A$$$ and a prefix of $$$B$$$ (the prefix of $$$A$$$ is written first, then the prefix of $$$B$$$)

Constraints:

$$$|A|,|B| <= 1e5$$$

both strings only have ASCII characters from $$$a$$$ to $$$z$$$

can some one come up with a solution, I would really appreciate it :D