Remove-Duplicates-ii.py

'''
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.

See Expected Output
'''
def removeDuplicates(self,head):
    dummy = prev = ListNode(0)
    dummy.next = head
    while head and head.next:
        if head.val == head.next.val:
            while head and head.next and head.val == head.next.val:
                head = head.next
            head = head.next
            prev.next  = head
        else:
            prev = prev.next
            head = head.next
    return dummy.next
s