freeCodeCamp/guide/english/certifications/coding-interview-prep/data-structures/learn-how-a-stack-works/index.md

title
Learn how a Stack Works

Learn how a Stack Works

Method:

• Stacks are an abstract data structures.
• They follow LIFO (Last In First Out) or FILO (First In Last Out) principle.
• Stack's insertion and deletion operations are of O(1) time complexity.
• In Javascript, arrays can be treated as a Stack since .push() and .pop() methods have time complexity of O(1).
• In this challenge we need to .pop() and then .push() into the stack.

Solution:

var homeworkStack = ["BIO12","HIS80","MAT122","PSY44"];

homeworkStack.pop();
homeworkStack.push("CS50");

Reference:

• Wikipedia
• Video by Hackerrank