反转链表

反转链表主要是靠三个指针，pre指向前一个指针，cur和next指向当前指针，保持这个顺序就可以。

function ReverseList(node){
let pre = null
let cur = node
let next = node
while(cur.next != null){
    next = cur.next
    cur.next = pre
    pre = cur
    cur = next
}
return pre
}