class Queue {
    constructor() {
        this.items = {}
        this.headIndex = 0
        this.tailIndex = 0
    }
    enqueue(item) {
        this.items[this.tailIndex] = item
        this.tailIndex++
    }
    dequeue() {
        if (!this.isEmpty) return
        const item = this.items[this.headIndex]
        delete this.items[this.headIndex]
        this.headIndex++
        return item
    }
    get length() {
        return this.tailIndex - this.headIndex
    }
    get isEmpty() {
        return this.tailIndex
    }
}