Reverse a singly linked list.

Example:

Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL
Follow up:

A linked list can be reversed either iteratively or recursively. Could you implement both?

題目分析：實(shí)現(xiàn)鏈表的倒置，以下是go語(yǔ)言的實(shí)現(xiàn)方法

func reverseList(head *ListNode) *ListNode {
    var help *ListNode
    var pre *ListNode
    for head != nil {
        help = head.Next
        head.Next = pre
        pre = head
        head =help
    }
    return pre
}