class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
class Solution(object):
def deleteDuplication(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
dummy = ListNode(-1)
dummy.next = head
p = dummy
while p.next:
cur = p.next
while cur and p.next.val == cur.val: cur = cur.next
if p.next.next == cur: p = p.next
else: p.next = cur
return dummy.next