Hi Codeforces community, can you help me to find the root of run time error in my solution for this problem 1428C - ABBB

Error is status_access_violation, google says it's something about pointers;

Submission link: 180179520

The approach is -> transform string to linked list of chars and when deleting two characters fix the "prev" for "next"; I generated "AB" strings up to 2^7, but it fails somewhere in 2^8, I'm not sure how to debug it; May be it's a memory leak issue?, I'm creating new pointers without deleting them, I tried using "delete pointer" but it did not help;