class LinkedListNode {
    constructor(element) {
        this.element = element  // 鏈表要存儲(chǔ)的值
        this.next = null        // 當(dāng)前節(jié)點(diǎn)的下一個(gè)節(jié)點(diǎn)
    }
}
let A = new LinkedListNode('A') // 第一個(gè)節(jié)點(diǎn)A
let B = new LinkedListNode('B') // 第二個(gè)節(jié)點(diǎn)B
let C = new LinkedListNode('C') // 第三個(gè)節(jié)點(diǎn)C
// 節(jié)點(diǎn)之間通過this.next屬性值連起來，如下：
A.next = B // 節(jié)點(diǎn)A下一個(gè)是節(jié)點(diǎn)B
B.next = C // 節(jié)點(diǎn)B下一個(gè)是節(jié)點(diǎn)C
console.log(A) // 輸出鏈表：A -> B -> C

class LinkedListNode {
    element: any
    next: (null | LinkedListNode)
    constructor(element: any) {
        this.element = element
        this.next = null
    }
}

class LinkedList {
    length: number
    head: (null | LinkedListNode)
    constructor() {
        this.length = 0
        this.head = null
    }
}

getLinkedListNode(index: number): (void | { [index: number]: (null | LinkedListNode) }) {
    if (this.isEmpty()) {
        throw new Error('LinkedList is empty')
    } else if (index < 0 || index >= this.length) {
        throw new Error(`${index} does exist in [0, ${this.length})`)
    } else if (index >= 0 && index < this.length) {
        let previous: (null | LinkedListNode) = null
        let current: (null | LinkedListNode) = this.head
        for (let i = 0; i < index; i++) {
            previous = current
            current = current!.next
        }
        return { 0: previous, 1: current, 2: current!.next }
    }
}

insert(element: any, index?: number): LinkedList {
    let node: (null | LinkedListNode) = new LinkedListNode(element)
    if (this.isEmpty()) {
        this.head = node
    } else if (index !== undefined && (index >= 0 && index < this.length)) {
        if (index === 0) {
            node.next = this.head
            this.head = node
        } else {
            let current: (void | object) = this.getLinkedListNode(index)
            node.next = current[0]!.next
            current[0]!.next = node
        }
    } else if (index !== undefined && (index < 0 || index > this.length)) {
        throw new Error(`${index} does exist in [0, ${this.length}]`)
    } else if (index === undefined || index === this.length) {
        let current: (null | LinkedListNode) = this.head
        while (current!.next !== null) {
            current = current!.next
        }
        current!.next = node
    }
    this.length++
    return this
}

remove(index: number): LinkedList {
    if (this.isEmpty()) {
        throw new Error('LinkedList is empty')
    } else {
        if (index === 0) {
            this.head = (this.length === 1) ? null : this.head!.next
        } else if (index > 0 && index < this.length) {
            let current: (void | object) = this.getLinkedListNode(index)
            current[0]!.next = (index + 1 === this.length) ? null : current[2]
        } else {
            throw new Error(`${index} does exist in [0, ${this.length})`)
        }
        this.length--
        return this
    }
}