JavaScript Exercises: N^th element from the bottom of the stack

JavaScript Stack: Exercise-17 with Solution

Nth Element from Bottom

Write a JavaScript program to get the n^th element from the bottom of the 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;
  }
  
 getNthFromBottom(n) {
    if (n < 1 || n > this.items.length)
      return "Invalid index";

    return this.items[n - 1];
  }
  
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("nth element from the bottom of the stack where n = "+n);
console.log(stack.getNthFromBottom(n));
n = 5;
console.log("nth element from the bottom of the stack where n = "+n);
console.log(stack.getNthFromBottom(n));
n = 7;
console.log("nth element from the bottom of the stack where n = "+n);
console.log(stack.getNthFromBottom(n));

Sample Output:

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

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-17 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that returns the nth element from the bottom of a stack by converting it to an array.
• Write a JavaScript function that computes the correct index from the bottom and retrieves the element without modifying the stack.
• Write a JavaScript function that uses recursion to access the nth element from the bottom of a linked list based stack.
• Write a JavaScript function that validates the value of n and handles cases when n is larger than the stack length.

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