Whereas a stack allows insertion and deletion of elements at only one end, and a queue allows insertion at one end and deletion at the other end, a deque (doubleended queue) allows insertion and deletion at both ends. Write four O(1) -time procedures to insert elements into and delete elements from both ends of a deque constructed from an array. | Numerade

Implement Queue using Stacks - GeeksforGeeks

The Queue data structure in a nutshell