/**
 * Simple Que using linked lists.
 * Pushed value can be anything.
 */
class Queue {
    constructor() {
        this.first = null;
        this.last = null;
        this.length = 0;
    }
    push(value) {
        const node = {
            value,
            next: null,
        };

        const prevLast = this.last;
        if (this.last !== null) {
            prevLast.next = node;
        }

        this.last = node;

        if (this.first === null) {
            this.first = node;
        }

        this.length += 1;
    }
    shift() {
        if (this.length === 0) return null;

        const shiftedFirst = this.first;

        this.first = shiftedFirst.next;
        this.length -= 1;

        return shiftedFirst.value;
    }
}