Read 10 ~ Stacks & Queues

By Abdallah obaid

NAME	URL
Home	Home.
Prep	Prep: Engineering Topics.
Read 01	Node Ecosystem, TDD, CI/CD.
Read 02	Classes, Inheritance, Functional.
Read 03	Data Modeling & NoSQL Databases.
Read 04	Advanced Mongo/Mongoose.
Read 05	Linked Lists.
Read 06	HTTP and REST.
Read 07	Express.
Read 08	Express Routing & Connected API.
Read 09	API Server.
Read 10	Stacks and Queues.
Read 11	Authentication.
Read 12	OAuth.
Read 13	Bearer Authorization.
Read 14	Access Control (ACL).
Read 15	Trees.
Read 16	Event Driven Applications.

---

Stacks & Queues

---

## Stacks:

• Stack is a linear data structure, consists of Nodes. Each Node references the next Node, but does not refer to previous node.
• Stack follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out).
• Common terminology for a stack is:
  1. Push: to add node.

  2. Pop: remove node

     if empty return exception.

  3. Top: top of the stack.

  4. Peek: used to view the top

     if empty return exception.

  5. IsEmpty: returns true when stack is empty otherwise returns false.
• When you push something to the stack, it becomes the new top.
• Pop remove Node from the top.
• The Big O for bush is O(1), it takes the same amount of time no matter how many Nodes (n)
• When we try to use pop we should check before if the stack empty or not with isEmpty.
• Peek can just check for the top node.
• With peek we need also to check if stack isEmpty to avoid the exception.

## Queue:

• Its also a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out).
• Common terminology for a queue is:
  1. Enqueue: Nodes or items that are added to the queue.
  2. Dequeue: Nodes or items that are removed from the queue. If called when the queue is empty an exception will be raised.
  3. Front: This is the front/first Node of the queue.
  4. Rear: This is the rear/last Node of the queue.
  5. Peek: When you peek you will view the value of the front Node in the queue. If called when the queue is empty an exception will be raised.
  6. IsEmpty: returns true when queue is empty otherwise returns false.