Given the head of a sorted singly linked list, remove every node whose value appears more than once, leaving only values that occur exactly once — the result must stay sorted. This is a stricter cousin of collapsing duplicates: instead of keeping one representative per repeated value, the entire run disappears. The optimal solution walks the list with a dummy node + prev/curr pairDummy Node + Prev/Curr PairA dummy node placed before head lets the very first node be unlinked the same way as any other, without special-casing "head might change." prev always trails the last node confirmed unique, so a discovered run can be skipped by pointing prev.next straight past it.: whenever curr's value matches the value right after it, the entire matching run — however long — is skipped in one relink; otherwise prev simply advances alongside curr.