JavaScript Exercises: Swap the top two elements of a stack

Last update on March 04 2025 09:36:11 (UTC/GMT +8 hours)

JavaScript Stack: Exercise-15 with Solution

Swap Top Two Elements

Write a JavaScript program to swap the top two elements of a given stack.

Sample Solution:

JavaScript Code:

class Stack {
  constructor() {
    this.items = [];
  }
  push(element) {
    this.items.push(element);
  }
  pop() {
    if (this.isEmpty()) {
      return "Underflow";
    }
    return this.items.pop();
  }
  peek() {
    return this.items[this.items.length - 1];
  }
  isEmpty() {
    return this.items.length === 0;
  }
  size() {
    return this.items.length;
  }
swap() {
    if (this.items.length < 2) {
      return "There are no sufficient elements.";
    }
    const topElement = this.items.pop();
    const secondElement = this.items.pop();
    this.items.push(topElement);
    this.items.push(secondElement);
  }  
displayStack(stack) {
  console.log("Stack elements are:");
  let str = "";
  for (let i = 0; i < stack.items.length; i++)
    str += stack.items[i] + " ";
  return str.trim();
 }      
}

let stack = new Stack();
stack.push(1);
stack.push(2);
stack.push(3);
stack.push(4);
stack.push(5);
stack.push(6);
stack.push(7);
console.log(stack.displayStack(stack));
console.log("Swap top two elements:");
stack.swap();
console.log(stack.displayStack(stack));
console.log("Input two more elements on the stack:")
stack.push(8);
stack.push(9);
console.log(stack.displayStack(stack));
console.log("Swap top two elements:");
stack.swap();
console.log(stack.displayStack(stack));

Sample Output:

Stack elements are:
1 2 3 4 5 6 7
Swap top two elements:
Stack elements are:
1 2 3 4 5 7 6
Input two more elements on the stack:
Stack elements are:
1 2 3 4 5 7 6 8 9
Swap top two elements:
Stack elements are:
1 2 3 4 5 7 6 9 8

Flowchart:

Live Demo:

For more Practice: Solve these Related Problems:

Write a JavaScript function that swaps the top two elements of a stack and returns the modified stack.
Write a JavaScript function that performs the swap operation using array destructuring without a temporary variable.
Write a JavaScript function that checks if the stack has at least two elements before attempting to swap.
Write a JavaScript function that logs the stack state before and after swapping the top two elements.

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