# Data structures stack and queue interview questions - stack and queue interview

## Describe stack operation.

Stack is a data structure that follows Last in First out strategy.
Stack Operations:-
Push – Pushes (inserts) the element in the stack. The location is specified by the pointer.
Pop – Pulls (removes) the element out of the stack. The location is specified by the pointer
Swap: - the two top most elements of the stack can be swapped
Peek: - Returns the top element on the stack but does not remove it from the stack
Rotate:- the topmost (n) items can be moved on the stack in a rotating fashion
A stack has a fixed location in the memory. When a data element is pushed in the stack, the pointer points to the current element

## Describe queue operation.

Queue is a data structure that follows First in First out strategy.
Queue Operations:
Push – Inserts the element in the queue at the end.
Pop – removes the element out of the queue from the front
Size – Returns the size of the queue
Front – Returns the first element of the queue.
Empty – to find if the queue is empty.

## Discuss how to implement queue using stack.

A queue can be implemented by using 2 stacks:-
1. An element is inserted in the queue by pushing it into stack 1
2. An element is extracted from the queue by popping it from the stack 2
3. If the stack 2 is empty then all elements currently in stack 1 are transferred to stack 2 but in the reverse order
4. If the stack 2 is not empty just pop the value from stack 2.

## Explain stacks and queues in detail.

A stack is a data structure based on the principle Last In First Out. Stack is container to hold nodes and has two operations - push and pop. Push operation is to add nodes into the stack and pop operation is to delete nodes from the stack and returns the top most node.

A queue is a data structure based on the principle First in First Out. The nodes are kept in an order. A node is inserted from the rear of the queue and a node is deleted from the front. The first element inserted in the first element first to delete.

## Question - What are priority queues?

A priority queue is essentially a list of items in which each item has associated with it a priority
Items are inserted into a priority queue in any, arbitrary order. However, items are withdrawn from a priority queue in order of their priorities starting with the highest priority item first.

Priority queues are often used in the implementation of algorithms

## Question - What is a circular singly linked list?

In a circular singly linked list, the last node of the list is made to point to the first node. This eases the traveling through the list.
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