[Leetcode]Remove Duplicates from Sorted List II

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.

把已经排好序的链表中重复出现过的元素全部删掉~  思路比较简单~

class Solution:
    # @param head, a ListNode
    # @return a ListNode
    def deleteDuplicates(self, head):
        if head is None: return None
        dummy = ListNode(0)
        dummy.next = head
        pre, cur = dummy, head
        while cur:
            while cur.next != None and cur.val == cur.next.val:
                cur = cur.next
            if pre.next != cur:
                pre.next = cur.next
            else:
                pre = pre.next
            cur = cur.next
        return dummy.next