In JavaScript, we could use array to work as both a Stack or a queue.

const arr = [1, 2, 3, 4]arr.push(5) // now array is [1, 2, 3, 4, 5]arr.pop() // 5, now the array is [1, 2, 3, 4]

Above code is a Stack, while below is a Queue

const arr = [1, 2, 3, 4]arr.push(5) // now the array is [1, 2, 3, 4, 5]arr.shift() // 1, now the array is [2, 3, 4, 5]

now suppose you have a stack, which has only follow interface:

class Stack {  push(element) { /* add element to stack */ }  peek() { /* get the top element */ }  pop() { /* remove the top element */}  size() { /* count of elements */}}

Could you implement a Queue by using only above Stack? A Queue must have following interface

class Queue {  enqueue(element) { /* add element to queue, similar to Array.prototype.push */ }  peek() { /* get the head element*/ }  dequeue() { /* remove the head element, similar to Array.prototype.pop */ }  size() { /* count of elements */ }}

note

you can only use Stack as provided, Array should be avoided for the purpose of practicing.

Watch videos for JavaScript Coding Question 13. Implement a Queue by using Stack

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13. Implement a Queue by using Stack