Suppose that you implement a queue using a null-terminated singly-linked list, maintaining a reference to the item least recently added (the front of the list) but not maintaining a reference to the item most recently added (the end of the list). What are the worst case running times for enqueue and dequeue?
constant time for both enqueue and dequeue
constant time for enqueue and linear time for dequeue
linear time for enqueue and constant time for dequeue
linear time for both enqueue and dequeue