算法题-翻转链表

interface LinkList {
    value:number;
    next?:LinkList
}
export function createLinkList(arr:number[]):LinkList|undefined {
    if(!arr.length) return
    let currentNode:LinkList = {
        value:arr[arr.length-1]
    }
    for (let i=arr.length-2;i>=0;i--){
        currentNode = {
            value:arr[i],
            next:currentNode
        }
    }
    return currentNode
}
// 1->2->3->4->5->6
// 6->5->4->3->2->1
export function reverseLinkList(data:LinkList|undefined):LinkList|undefined {
    if(!data) return
    let preNode:LinkList|undefined
    let currentNode:LinkList|undefined
    let nextNode:LinkList|undefined = data
    while (nextNode){
        if(currentNode && !preNode){
            currentNode.next = undefined
        }
        if(preNode && currentNode) {
            currentNode.next = preNode
        }
        preNode = currentNode
        currentNode = nextNode
        nextNode = nextNode.next
    }
    currentNode!.next = preNode
    return currentNode
}