leetcode 83 删除排序链表中的重复元素

# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class (object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head
        pre = head
        p = head.next
        while p:
            while p and p.val == pre.val:
                p = p.next
            if not p:
                break
            else:
                pre = pre.next
                pre.val = p.val
                p = p.next
        pre.next = None
        return head