Stack Implementation

What is Stack Implementation Using Array?

A stack is a linear data structure that follows the LIFO (Last In First Out) principle. Arrays provide a simple way to implement stack operations with constant time complexity.

Core Stack Operations

push(item)
pop()
peek()
isEmpty()
isFull()

Algorithmic Steps

Stack Basic Operations

Initialize Stack

  1. Create an empty array to store elements
  2. Initialize top pointer/index to -1
  3. Optional: Set maximum size limit

push()

  1. Check if stack is full
  2. If full, return "Stack Overflow"
  3. Increment top pointer
  4. Store element at array[top]

pop()

  1. Check if stack is empty
  2. If empty, return "Stack Underflow"
  3. Access element at array[top]
  4. Decrement top pointer
  5. Return the element

Stack Helper Operations

peek()

  1. Check if stack is empty
  2. If empty, return null
  3. Return array[top] without removal

isEmpty()

  1. Return true if top pointer is -1
  2. Return false otherwise

isFull()

  1. Return true if top equals (max_size - 1)
  2. Return false otherwise

Visual Representation

42
17
8 (top)
Stack after operations: push(42), push(17), push(8)

Time Complexity

OperationComplexity
push()O(1)
pop()O(1)
peek()O(1)
isEmpty()O(1)

Key Characteristics

  • LIFO Principle: Last element added is first removed
  • Dynamic Size: Can grow until memory limits
  • Efficiency: All operations work in constant time
  • Versatility: Foundation for many algorithms

Stack Implementation using Array

// Stack Implementation using Array (JavaScript)
class Stack {
  constructor(size = 10) {
    this.items = new Array(size);
    this.top = -1;
    this.capacity = size;
  }

  // Push operation
  push(element) {
    if (this.isFull()) {
      console.log("Stack Overflow");
      return;
    }
    this.items[++this.top] = element;
  }

  // Pop operation
  pop() {
    if (this.isEmpty()) {
      console.log("Stack Underflow");
      return undefined;
    }
    return this.items[this.top--];
  }

  // Peek operation
  peek() {
    if (this.isEmpty()) {
      console.log("Stack is empty");
      return undefined;
    }
    return this.items[this.top];
  }

  // Check if stack is empty
  isEmpty() {
    return this.top === -1;
  }

  // Check if stack is full
  isFull() {
    return this.top === this.capacity - 1;
  }

  // Get stack size
  size() {
    return this.top + 1;
  }

  // Print stack contents
  print() {
    if (this.isEmpty()) {
      console.log("Stack is empty");
      return;
    }
    console.log("Stack contents:");
    for (let i = this.top; i >= 0; i--) {
      console.log(this.items[i]);
    }
  }
}

// Usage
const stack = new Stack(5);
stack.push(10);
stack.push(20);
stack.push(30);
console.log("Top element:", stack.peek()); // 30
console.log("Stack size:", stack.size());  // 3
stack.print();
stack.pop();
console.log("After pop, top element:", stack.peek()); // 20

Explore other implementation

Using Linked List