# JavaScript Exercises: Move the nth element from the top of the stack to the top

## JavaScript Stack: Exercise-18 with Solution

Write a JavaScript program to implement a stack and move the nth element from the top of the stack to the top.

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;
}
moveNthToTop(n) {
if (this.items.length == 0) {
return this.items;
}
if (n > this.items.length) {
return this.items;
}
let tempStack = [];
for (let i = 0; i < n - 1; i++) {
tempStack.push(this.items.pop());
}
let nthElement = this.items.pop();
while (tempStack.length > 0) {
this.items.push(tempStack.pop());
}
tempStack.push(nthElement);
while (this.items.length > 0) {
tempStack.push(this.items.pop());
}
while (tempStack.length > 0) {
this.items.push(tempStack.pop());
}
return this.items;
}
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(100);
stack.push(200);
stack.push(300);
stack.push(400);
stack.push(500);
stack.push(600);
stack.push(700);
console.log(stack.displayStack(stack));
n = 2;
console.log("Move the nth element from the top of the stack to the top, where n = "+n);
stack.moveNthToTop(n)
console.log(stack.displayStack(stack));
n = 5;
console.log("Move the nth element from the top of the stack to the top, where n = "+n);
stack.moveNthToTop(n)
console.log(stack.displayStack(stack));
n = 7;
console.log("Move the nth element from the top of the stack to the top, where n = "+n);
stack.moveNthToTop(n)
console.log(stack.displayStack(stack));

Sample Output:

Stack elements are:
100 200 300 400 500 600 700
Move the nth element from the top of the stack to the top, where n = 2
Stack elements are:
100 200 300 400 500 700 600
Move the nth element from the top of the stack to the top, where n = 5
Stack elements are:
100 200 400 500 700 600 300
Move the nth element from the top of the stack to the top, where n = 7
Stack elements are:
200 400 500 700 600 300 100

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-18 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus

Stack Previous: Nth element from the bottom of the stack.
Stack Exercises Next: Move the nth element from the bottom of the stack to the top.

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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]