反转链表

leetcode206题: https://leetcode-cn.com/problems/reverse-linked-list/submissions/

var reverseList = function(head) {
    if (!head || !head.next) {
        return head
    }

    let pre = null
    let cur = head
    let next
    // 借助临时变量，按层次依次赋值，实现变量移动
    while (cur) {
        next = cur.next
        cur.next = pre
        pre = cur
        cur = next
    }
    return pre
};