queue-from-stacks.js

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

    push(value) {
        this.array.push(value)
    }

    pop() {
        return this.array.pop()
    }

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

class Queue {
    constructor() {
        this.s1 = new Stack()
        this.s2 = new Stack()
    }

    enqueue(value) {
        this.s1.push(value)
    }

    dequeue() {
        if (!this.s2.isEmpty) {
            return this.s2.pop()
        }
        while (!this.s1.isEmpty()) {
            this.s2.push(this.s1.pop())
        }
        return this.s2.pop()
    }
}