Stack：
Abstract data type with the following operations:
Push(Key); Key Top(); Key Pop(); Boolean Empty().
Two form of Stack:
Stack with Array; Stack with Linked list.
Summary:
Stacks can be implemented with either an array or a linked list.
Each stack operation is O(1): Push, Pop, Top, Empty.
Stacks are occasionally known as LIFO queues.
Queue：
Abstract data type with the following operations:
Enqueue(Key); Key Dequeue(); Boolean Empty()
FIFO.
Implementation with Linked List:
Enqueue: use List.PushBack
Dequeue: use List.TopFront and List.PopFront
Empty: use List.Empty
Implementation with Array:
At this time, If operation of Enqueue cannot push "g" into the space，because we need to leave one space to recognize where is head and where is tail.
Summary:
Queues can be implemented with either a Linked list (with tail pointer) or an array.
Each queue operation is O(1): Enqueue, Dequeue, Empty.