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.

Example

Given 1->2->3->3->4->4->5, return 1->2->5.

Given 1->1->1->2->3, return 2->3.

Solution

循环删除重复节点：

while head.next != None and val == head.next.val:

head.next = head.next.next

删除重复节点的前提是排序过的链表，如果没有排序，使用Hashtable，如果把重复的留一个，不需要使用Dummy 否则使用。

"""
Definition of ListNode
class ListNode(object):

    def __init__(self, val, next=None):
        self.val = val
        self.next = next
"""
class Solution:
    """
    @param head: A ListNode
    @return: A ListNode
    """
    def deleteDuplicates(self, head):
        if head == None or head.next == None:
            return head
        dummy = ListNode(0)
        dummy.next = head
        head = dummy

        while head.next and head.next.next:
            if head.next.val == head.next.next.val:
                val = head.next.val
                while head.next and head.next.val == val:
                    head.next = head.next.next
            else:
                head = head.next

        return dummy.next