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?
题目分析：实现链表的倒置，以下是go语言的实现方法
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
}
