<pre class="shiki github-dark shaku"><code>/* you can use this Class which is bundled together with your codeclass Stack { push(element) { // add element to stack } peek() { // get the top element } pop() { // remove the top element} size() { // count of element }}*//* Array is disabled in your code */// you need to complete the following Classclass Queue { constructor() { this.primaryStack = new Stack(); this.overflowStack = new Stack(); } enqueue(element) { this.primaryStack.push(element); } peek() { if(this.overflowStack.size() &gt; 0) { return this.overflowStack.peek(); } // get the bottom element in primaryStack while (this.primaryStack.size() &gt; 0) { // run loop till all elements of primaryStack are copied to overflowStack this.overflowStack.push(this.primaryStack.pop()); } return this.overflowStack.peek(); } size() { return this.primaryStack.size() + this.overflowStack.size(); } dequeue() { if(this.overflowStack.size() &gt; 0) { return this.overflowStack.pop(); } while(this.primaryStack.size() &gt; 0) { this.overflowStack.push(this.primaryStack.pop()); } return this.overflowStack.pop(); }}</code></pre>

dequeue is O(n) complexity. O(n) space complexity.

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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() // …