Remove Duplicates from Sorted List II

题目：

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

.
代码：
# Definition for singly-linked list.

# class ListNode:

# def __init__(self, x):

# self.val = x

# self.next = None

class Solution:

# @param {ListNode} head

# @return {ListNode}

def deleteDuplicates(self, head):

sentry = ListNode(-1)

sentry.next = head

pre,now = sentry,head

while now and now.next:

if now.val==now.next.val:

now = now.next

while now.next and now.val==now.next.val:

now=now.next

now = now.next

pre.next = now

else:

pre = now

now = now.next

return sentry.next