JavaScript Exercises: Middle element(s) of a stack

JavaScript Stack: Exercise-13 with Solution

Middle Element(s) of Stack

Write a JavaScript program to get the middle element(s) 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;
  }
  getMiddleElements() {
    let middleIndex = Math.floor(this.size() / 2);
    let middleElements = [];
    if (this.size() % 2 === 0) {
      middleElements.push(this.items[middleIndex - 1]);
    }
    middleElements.push(this.items[middleIndex]);
    return middleElements;
  }  
  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);
console.log(stack.displayStack(stack));
console.log("Middle element(s):");
console.log(stack.getMiddleElements());
console.log("Add one more element:");
stack.push(4);
console.log(stack.displayStack(stack));
console.log("Middle element(s):");
console.log(stack.getMiddleElements());
console.log("Add two more elements:");
stack.push(5);
stack.push(6);
console.log(stack.displayStack(stack));
console.log("Middle element(s):");
console.log(stack.getMiddleElements());
console.log("Add one more element:");
stack.push(7);
console.log(stack.displayStack(stack));
console.log("Middle element(s):");
console.log(stack.getMiddleElements());

Sample Output:

Stack elements are:
1 2 3
Middle element(s):
[2]
Add one more element:
Stack elements are:
1 2 3 4
Middle element(s):
[2,3]
Add two more elements:
Stack elements are:
1 2 3 4 5 6
Middle element(s):
[3,4]
Add one more element:
Stack elements are:
1 2 3 4 5 6 7
Middle element(s):
[4]

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-13 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that retrieves the middle element(s) from a stack and returns them without altering the stack.
• Write a JavaScript function that computes the middle index of a stack implemented as an array and handles both even and odd lengths.
• Write a JavaScript function that uses recursion to locate and return the middle element of a stack.
• Write a JavaScript function that returns an array of middle elements when the stack has an even number of elements.

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