[b3b0p]

I also was able to solve it in a couple/few min after seeing the comment. I did have a couple issues, index was off by one, and didn't catch an issue if I had already seen the substring using a brute force nested loop, but otherwise it works (Python). Edit: I also did it without a nested loop using a dictionary. Why I didn't think of this initially I don't know.

I've also had a couple FAANG onsites and get nervous as can be, but that's just a practice more and be more confident with my abilities problem I feel. No offers though yet. Still trying and practicing.