原题地址：https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list-ii/
题意：
Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.
解题思路：链表的基本操作。
代码：
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None class Solution:
# @param head, a ListNode
# @return a ListNode
def deleteDuplicates(self, head):
if head == None or head.next == None:
return head
dummy = ListNode(0); dummy.next = head
p = dummy
tmp = dummy.next
while p.next:
while tmp.next and tmp.next.val == p.next.val:
tmp = tmp.next
if tmp == p.next:
p = p.next
tmp = p.next
else:
p.next = tmp.next
return dummy.next