写一个单向链数据结构的 js 实现并标注复杂度

class ListNode {
    constructor(val) {
        this.val = val
        this.next = null
    }
}

class LinkedList {
    head = null
    tail = null
    size = 0

    // 时间复杂度O(n)
    get = index => {
        if (index < 0) return -1
        let node = this.head
        for (let i = 0; i < index; i++) {
            if (!node) return -1
            node = node.next
        }
        return node ? node.val : -1
    }

    // 时间复杂度O(1)
    addAtHead = val => {
        const node = new ListNode(val)
        if (!this.head) {
            this.head = this.tail = node
        } else {
            node.next = this.head
            this.head = node
        }
        this.size++
    }

    // 时间复杂度O(1)
    addAtTail = val => {
        const node = new ListNode(val)
        if (!this.tail) {
            this.head = this.tail = node
        } else {
            this.tail.next = node
            this.tail = node
        }
        this.size++
    }

    // 时间复杂度O(n)
    addAtIndex = (index, val) => {
        const node = new ListNode(val)
        if (index > this.size) return
        if (index === this.size) return this.addAtTail(val)
        if (index <= 0) return this.addAtHead(val)
        let head = this.head
        for (let i = 1; i < index; i++) {
            if (!head) return
            head = head.next
        }
        node.next = head.next
        head.next = node
        this.size++
    }

    // 时间复杂度O(n)
    deleteAtIndex = index => {
        let head = this.head
        if (!head || index >= this.size || index < 0) return
        if (index === 0) {
            if (this.size === 1) {
                this.head = this.tail = null
            } else {
                this.head = this.head.next
            }
            this.size--
            return
        }
        for (let i = 1; i < index; i++) {
            if (!head) return
            head = head.next
        }
        if (!head) return
        if (head.next) {
            if (head.next === this.tail) {
                this.tail = head
                head.next = null
            } else {
                head.next = head.next.next
            }
        } else {
            this.head = this.tail = null
        }
        this.size--
    }
}