Delete Node in a Linked List (O(1) trick)

To solve this efficiently in constant time without access to the head, I would use the 'copy-and-skip' approach. Since we cannot update the previous node's pointer to skip the current one, we simulate deletion by overwriting the current node's data with the data from the next node. Once the current node holds the next node's value, we simply redirect the current node's next pointer to point to the node after the next one, effectively removing the original next node from the chain. For example, consider a list 1 -> 2 -> 3 -> 4 where we need to delete node 2. We copy the value 3 into node 2, making it 1 -> 3 -> 3 -> 4. Then, we update node 2's next pointer to skip the second 3, pointing directly to 4. The result is 1 -> 3 -> 4, achieving the desired outcome in O(1) time. However, I must highlight a critical edge case: if the node to be deleted is the tail, this approach fails because there is no next node to copy from. In that specific scenario, we would technically need to traverse back or mark the node as invalid, but since the problem guarantees an O(1) solution, we assume the input node is not the tail. This technique demonstrates deep knowledge of linked list mechanics and the trade-offs involved when pointer references are restricted.