Implement a queue by using a singly linked list
L. The operations
DEQUEUEshould still take $\O(1)$ time.
This is also too simple to be worth implementing.
ENQUEUE operation inserts an element in the beginning of the list and
DEQUEUE operation removes an element from the end of the list. In this
case we need to keep track of the last element of the list. We can do that
with a sentinel.