82. 删除排序链表中的重复元素 II

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        h = ListNode(-1)
        h.next = head
        pre = h
        cur = head
        while cur != None: 
            duplicate = False          
            while cur.next != None and cur.val == cur.next.val:
                cur = cur.next
                duplicate = True

            if duplicate == False:
                pre = cur
            else:
                pre.next = cur.next

            cur = cur.next

        return h.next