1+ # Definition for singly-linked list.
2+ # class ListNode:
3+ # def __init__(self, val=0, next=None):
4+ # self.val = val
5+ # self.next = next
6+ class Solution :
7+ def mergeTwoLists (self , list1 : Optional [ListNode ], list2 : Optional [ListNode ]) -> Optional [ListNode ]:
8+ # Create a dummy node for our result list
9+ resultList = ListNode ()
10+ 11+ # Like a pointer to the last node on the list, which we can use to add more elemets to the list.
12+ resultListCurrent = resultList
13+ 14+ # Handle cases of one or both lists being empty
15+ if list1 is None and list2 is None :
16+ return None
17+ 18+ if list1 is None and list2 is not None :
19+ return list2
20+ 21+ if list2 is None and list1 is not None :
22+ return list1
23+ 24+ while (list1 is not None ) and (list2 is not None ):
25+ if list1 .val <= list2 .val :
26+ resultListCurrent .next = list1
27+ list1 = list1 .next
28+ else :
29+ resultListCurrent .next = list2
30+ list2 = list2 .next
31+ 32+ resultListCurrent = resultListCurrent .next
33+ 34+ # One of the two list pointers will be None.
35+ # Add the remaining elements of the non-empty list to the result list
36+ if list1 is not None :
37+ while list1 is not None :
38+ resultListCurrent .next = list1
39+ list1 = list1 .next
40+ resultListCurrent = resultListCurrent .next
41+ elif list2 is not None :
42+ while list2 is not None :
43+ resultListCurrent .next = list2
44+ list2 = list2 .next
45+ resultListCurrent = resultListCurrent .next
46+ 47+ # Return result list without dummy node
48+ return resultList .next
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