Stack

Peek Operation

Peek Operation

Returns the topmost element from the stack without removing it.

Example: Peeking at a stack

  1. Current stack: [7, 3, 5]
  2. Peek → returns 7: [7, 3, 5] (stack remains unchanged)
  3. After pop: [3, 5]
  4. Peek → returns 3: [3, 5]
  • Time Complexity: O(1)
  • Space Complexity: O(1)

Time Complexity Analysis

The peek operation is useful when you need to inspect the top element before deciding whether to pop it or push another element onto the stack.

Daily DSA Challenge By Hello World

Visualize Push, Pop, and Peek operations

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Stack Quiz Challenge

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Stack Push & Pop Implementation

// Stack Implementation with Peek Operation in JavaScript
class Stack {
  constructor() {
    this.items = [];
    this.top = -1;
  }

  // Push operation
  push(element) {
    this.items[++this.top] = element;
    console.log(`Pushed: ${element}`);
  }

  // Pop operation
  pop() {
    if (this.isEmpty()) {
      console.log("Stack Underflow");
      return -1;
    }
    return this.items[this.top--];
  }

  // Peek operation
  peek() {
    if (this.isEmpty()) {
      console.log("Stack is empty");
      return -1;
    }
    console.log(`Top element: ${this.items[this.top]}`);
    return this.items[this.top];
  }

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

  // 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.peek();
stack.pop();
stack.peek();

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