1.考虑输入空链表和一个节点链表

2.如果头节点不重复，直接递归查找重复

3.双指针，进行判断两个节点是不是相等

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def deleteDuplication(self, pHead):
        # write code here
        if pHead is None or pHead.next is None:
            return pHead
        head1 = pHead.next
        if head1.val != pHead.val:
            pHead.next = self.deleteDuplication(pHead.next)
        else:
            while pHead.val == head1.val and head1.next is not None:
                head1 = head1.next
            if head1.val != pHead.val:
                pHead = self.deleteDuplication(head1)
            else:
                return None
        return pHead