Method popleft

javascript/0460-lfu-cache.js:36–42

()

    }

    popleft() {
        let data = this.Left.next.val;
        this.Left.next = this.Left.next.next;
        this.Left.next.prev = this.Left;
        this.map.delete(data);
        return data;
    }

    pushRight(val) {
        let newNode = new ListNode(val, this.Right);