Refactor : use list1&& list2 instead make new instance

Author: sungjinwi

merge-two-sorted-lists/sungjinwi.py

@@ -23,10 +23,10 @@ def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) ->
 
         while list1 and list2 :
             if list1.val < list2.val :
-                node.next = ListNode(list1.val)
+                node.next = list1
                 list1 = list1.next
             else :
-                node.next = ListNode(list2.val)
+                node.next = list2
                 list2 = list2.next
             node = node.next
         node.next = list1 or list2