Q23 Merge k Sorted Lists - python

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:
        
        if not lists or len(lists) == 0:
            return None
        while len(lists) > 1:
            MergedLists = []
            for i in range(0, len(lists), 2):
                l1 = lists[i]
                l2 = lists[i + 1] if (i + 1) < len(lists) else None
                MergedLists.append(self.MergeList(l1, l2))    
            lists = MergedLists
        return lists[0]     
        
    def MergeList(self, l1, l2):
        dummy = ListNode()
        tail = dummy
        while l1 and l2:
            if l1.val < l2.val:
                tail.next = l1
                l1 = l1.next
            else:
                tail.next = l2
                l2 = l2.next
            tail = tail.next
        if l1:
            tail.next = l1
        elif l2:
            tail.next = l2
        return dummy.next