JavaScript Exercises: Swap the top two elements of a stack
JavaScript Stack: Exercise-15 with Solution
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:
See the Pen javascript-stack-exercise-15 by w3resource (@w3resource) on CodePen.
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Stack Previous: Remove a specific element from a stack.
Stack Exercises Next: Nth element from the top of the stack.
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JavaScript: Tips of the Day
Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function
Example:
const tips_unzip = (arr, fn) => arr .reduce( (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc), Array.from({ length: Math.max(...arr.map(x => x.length)) }).map(x => []) ) .map(val => fn(...val)); console.log(tips_unzip([[2, 15, 200], [3, 25, 300]], (...args) => args.reduce((acc, v) => acc + v, 0)));
Output:
[5, 40, 500]
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