Given the head of a sorted singly linked list, collapse every run of equal values down to a single node, and return the resulting (still sorted) list. Since the list arrives sorted, any two nodes holding the same value are guaranteed to sit right next to each other — there's no need to search the whole list for matches. The optimal solution uses this adjacent-duplicate checkAdjacent-Duplicate CheckWhen a sequence is sorted, every group of equal values forms one contiguous run. Detecting a duplicate then only requires comparing each element to its immediate neighbor, rather than checking it against everything seen so far.: one pointer walks the list, and whenever the very next node repeats the current value, it's unlinked in place — no extra memory, no full re-scan.