Stack and queue

Stack and queue are the simplest of complex data structures.

There are two basic methods for organizing the manipulation of a data structure:

1. FIFO (First In First Out),
2. LIFO (Last In Last Out).

FIFO - is a method of organizing the manipulation of a data structure (queue), where elements that we choose are inserted into the end (tail) of structure and extracted of the entry (head) of structure solely.

LIFO - is a method of organizing the manipulation of a data structure (stack), where elements that we choose are inserted and extracted into / from the end of structure solely.

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Stack - is a data structure that is orginised according to the principe of LIFO. Queue - is a data structure that is orginised according to the principe of FIFO.

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Methods and difficulties

STACK:

1. push()

PURPOSE: to add element into the end (top) of the stack. DIFFICULTY: O(1).

2. pop()

PURPOSE: to return element of the end (top) of the stack. DIFFICULTY: O(1).

3. peek()

PURPOSE: to return element of the end (top) of the stack but doesn't delete this item. DIFFICULTY: O(1).

4. count()

PURPOSE: to return a number of a quantity of elements of the stack (depth of the stack). DIFFICULTY: O(1).

P.S. We are going to use an array for easy reading but an usage a linked list is better because the linked list allows to improve our structure.