optimize merge-two-sorted-lists

Author: parkhojeong

merge-two-sorted-lists/parkhojeong.py

@@ -5,31 +5,21 @@
 #         self.next = next
 class Solution:
     def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
-        if not list1:
-            return list2
-        if not list2:
-            return list1
-
-
-        if list1.val > list2.val:
-            list1, list2 = list2, list1
-
-        head = list1
+        dummy_head = ListNode()
+        cur = dummy_head
 
         while list1 and list2:
-            if not list1.next:
-                list1.next = list2
-                break
-
-
-            if list2.val <= list1.next.val:
-                list2_next = list2.next
-
-                list2.next = list1.next
-                list1.next = list2
-                list2 = list2_next
-            else:
+            if list1.val <= list2.val:
+                cur.next = list1
                 list1 = list1.next
+            else:
+                cur.next = list2
+                list2 = list2.next
+            cur = cur.next
 
+        if list1:
+            cur.next = list1
+        elif list2:
+            cur.next = list2
 
-        return head
+        return dummy_head.next