Python solution give this hint as input type
""" :type lists: List[ListNode] :rtype: ListNode """
but the test input has an example: [ [ ] ]
I don't understand why there is a  in a , I think it should be
[ ListNode1, ListNode2 ... ] at least it should not be  but a None, or ListNode is an object like:
# Definition for singly-linked list. # class ListNode(object): # def __init__(self, x): # self.val = x # self.next = None
Am I misunderstand something?