JavaScript Exercises: Find the maximum and minimum elements in a stack (using an array)

JavaScript Stack: Exercise-5 with Solution

Max & Min in Stack

Write a JavaScript program to find the maximum and minimum elements in a stack.

Sample Solution:

JavaScript Code:

class Stack {
  constructor() {
    this.items = [];
    this.maxStack = [];
    this.minStack = [];
  }

  // Pushes an element onto the stack
  push(element) {
    this.items.push(element);

    if (this.maxStack.length == 0 || element >= this.maxStack[this.maxStack.length - 1]) {
      this.maxStack.push(element);
    }

    if (this.minStack.length == 0 || element <= this.minStack[this.minStack.length - 1]) {
      this.minStack.push(element);
    }
  }

  // Removes the top element from the stack and returns it
  pop() {
    if (this.items.length == 0)
      return "Underflow";
    
    const poppedElement = this.items.pop();

    if (poppedElement == this.maxStack[this.maxStack.length - 1]) {
      this.maxStack.pop();
    }

    if (poppedElement == this.minStack[this.minStack.length - 1]) {
      this.minStack.pop();
    }

    return poppedElement;
  }

  // Returns the top element of the stack
  peek() {
    if (this.items.length == 0)
      return "No elements in Stack";
    return this.items[this.items.length - 1];
  }

  // Checks if the stack is empty
  isEmpty() {
    return this.items.length == 0;
  }

  // Returns the number of elements in the stack
  size() {
    return this.items.length;
  }

  // Find the maximum value in the stack
  getMax() {
    if (this.maxStack.length == 0)
      return "No elements in Stack";
    return this.maxStack[this.maxStack.length - 1];
  }

  // Find the minimum value in the stack
  getMin() {
    if (this.minStack.length == 0)
      return "No elements in Stack";
    return this.minStack[this.minStack.length - 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();
  }
}

console.log("Initialize a stack:")
let stack = new Stack();
console.log("Input some elements on the stack:")
stack.push(1);
stack.push(9);
stack.push(3);
stack.push(4);
stack.push(-5);
console.log(stack.displayStack(stack));
console.log("Maximum value in the stack:");
console.log(stack.getMax());
console.log("Minimum value in the stack:");
console.log(stack.getMin());
console.log("Remove one element from the stack:")
stack.pop();
console.log(stack.displayStack(stack));
console.log("Maximum value in the stack:");
console.log(stack.getMax());
console.log("Minimum value in the stack:");
console.log(stack.getMin());

Sample Output:

Initialize a stack:
Input some elements on the stack:
Stack elements are:
1 9 3 4 -5
Maximum value in the stack:
9
Minimum value in the stack:
-5
Remove one element from the stack:
Stack elements are:
1 9 3 4
Maximum value in the stack:
9
Minimum value in the stack:
1

Flowchart:

Live Demo:

See the Pen javascript-stack-exercise-5 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that traverses a stack to find and return both the maximum and minimum elements simultaneously.
• Write a JavaScript function that maintains auxiliary stacks to keep track of the maximum and minimum elements as items are pushed and popped.
• Write a JavaScript function that computes the max and min in a stack recursively without altering the original stack.
• Write a JavaScript function that returns an object with properties max and min by iterating through the stack only once.

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