NC78 反转链表

输入一个链表，反转链表后，输出新链表的表头。

此题有四种解法，具体可参考：

http://c.biancheng.net/view/8105.html

给出我个人最喜欢的一种：头插法

class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        newHead = None

        if pHead == None or pHead.next == None:
            return pHead
        
        while pHead != None:
            temp = pHead 
            # delete old node
            pHead = pHead.next
            # add node to the new list
            temp.next = newHead
            newHead = temp
            
        return newHead