Stack Push & Pop

What is Stack Push & Pop?

Push and Pop are the two fundamental operations in stack data structure. Stack follows LIFO (Last In First Out) principle - the last element added is the first one to be removed.

Push Operation

Adds an element to the top of the stack.

Example: Pushing elements onto a stack

Start with empty stack: [ ]
Push 5: [5]
Push 3: [3, 5]
Push 7: [7, 3, 5]

Time Complexity: O(1)
Space Complexity: O(1)

Pop Operation

Removes and returns the topmost element from the stack.

Example: Popping elements from a stack

Current stack: [7, 3, 5]
Pop → returns 7: [3, 5]
Pop → returns 3: [5]
Pop → returns 5: [ ]

Time Complexity: O(1)
Space Complexity: O(1)

Stack Underflow & Overflow

Stack Underflow: Trying to pop from an empty stack
Stack Overflow: Trying to push to a full stack (in fixed-size implementations)

Real-world Applications

Function call management in programming languages (call stack)
Undo/Redo operations in text editors
Back/Forward navigation in web browsers
Expression evaluation and syntax parsing
Memory management

Push and Pop operations are fundamental to stack functionality. While simple to implement, stacks are powerful data structures used in many algorithms and system designs.

Visualize the LIFO (Last In, First Out) principle

Stack Visualization

Stack is empty

Test Your Knowledge before moving forward!

Stack Quiz Challenge

How it works:

+1 point for each correct answer
0 points for wrong answers
-0.5 point penalty for viewing explanations
Earn stars based on your final score (max 5 stars)

Stack Push & Pop Implementation

// Stack Implementation with Push/Pop in JavaScript
class Stack {
  constructor() {
    this.items = [];
    this.top = -1;
    this.MAX_SIZE = 10;
  }

  // Push operation
  push(element) {
    if (this.top >= this.MAX_SIZE - 1) {
      console.log("Stack Overflow");
      return;
    }
    this.items[++this.top] = element;
    console.log(`Pushed: ${element}`);
  }

  // Pop operation
  pop() {
    if (this.top < 0) {
      console.log("Stack Underflow");
      return -1;
    }
    const element = this.items[this.top--];
    console.log(`Popped: ${element}`);
    return element;
  }

  // Display stack
  display() {
    console.log("Current Stack:", this.items.slice(0, this.top + 1));
  }
}

// Usage
const stack = new Stack();
stack.push(10);
stack.push(20);
stack.push(30);
stack.display();
stack.pop();
stack.display();