232. Implement Queue using Stacks (COSTLY DEQUEUE)

/**
* Problem statement: https://leetcode.com/problems/implement-queue-using-stacks/description/
*
* Notes: This implementation prioritizes efficiency for enqueuing (adding)
* items from the queue, with a constant time complexity (O(1)).
* Dequeuing (removing) or peeking an item from the queue has a linear time complexity (O(n)).
*
**/

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

    push(item) {
        this.items.push(item);
    }

    pop() {
        return this.items.pop();
    }

    peek() {
        return this.items[this.items.length - 1];
    }

    isEmpty() {
        return !this.items.length
    }

    size() {
        return this.items.length();
    }
}



class MyQueue {
    constructor() {
        this.queueStack = new Stack();
        this.helperStack = new Stack();
    }

    push(item) {
        // EFFICIENT ENQUEUE
        this.queueStack.push(item);
    }

    pop() {
        // COSTLY DEQUEUE

        // move all items from queueStack to helperStack
        while(!this.queueStack.isEmpty()) {
            this.helperStack.push(this.queueStack.pop());
        }

        // deQueue item from top of helperStack
        const dequeuedItem = this.helperStack.pop();

        // move all items back to queueStack from helperStack
        while(!this.helperStack.isEmpty()) {
            this.queueStack.push(this.helperStack.pop());
        }

        return dequeuedItem;
    }

    peek() {
        // COSTLY PEEK
        while(!this.queueStack.isEmpty()) {
            this.helperStack.push(this.queueStack.pop());
        }

        const peekedItem = this.helperStack.peek();

        while(!this.helperStack.isEmpty()) {
            this.queueStack.push(this.helperStack.pop());
        }

        return peekedItem;
    }

    empty() {
        return this.queueStack.isEmpty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * var obj = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */