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

JavaScript Stack: Exercise-18 with Solution

Move Nth from Top to Top

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.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that moves the nth element from the top of a stack to the top position using intermediate storage.
• Write a JavaScript function that rotates the stack so that the nth element becomes the new top, preserving the order of other elements.
• Write a JavaScript function that implements the operation recursively without creating a new stack.
• Write a JavaScript function that validates the index n before performing the move operation and returns an error if invalid.

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