Add problem 21 - Merge Two Sorted Lists

Author: anirudhology

problems/linked_list/merge_two_sorted_lists.py

@@ -0,0 +1,41 @@
+from typing import Optional
+
+from problems.util.list_node import ListNode
+
+
+class MergeTwoSortedLists:
+    @staticmethod
+    def mergeTwoLists(head1: Optional[ListNode], head2: Optional[ListNode]) -> Optional[ListNode]:
+        # Special cases
+        if head1 is None:
+            return head2
+        if head2 is None:
+            return head1
+        # Head of the resultant list
+        if head1.val < head2.val:
+            head = ListNode(head1.val)
+            head1 = head1.next
+        else:
+            head = ListNode(head2.val)
+            head2 = head2.next
+        # Pointer to traverse through the resultant list
+        temp = head
+        # Process both lists together
+        while head1 is not None and head2 is not None:
+            if head1.val < head2.val:
+                temp.next = ListNode(head1.val)
+                head1 = head1.next
+            else:
+                temp.next = ListNode(head2.val)
+                head2 = head2.next
+            temp = temp.next
+        # Process remaining nodes in lists
+        while head1 is not None:
+            temp.next = ListNode(head1.val)
+            head1 = head1.next
+            temp = temp.next
+        while head2 is not None:
+            temp.next = ListNode(head2.val)
+            head2 = head2.next
+            temp = temp.next
+        return head

tests/linked_list/merge_two_sorted_lists_test.py

@@ -0,0 +1,37 @@
+import unittest
+
+from problems.linked_list.merge_two_sorted_lists import MergeTwoSortedLists
+from problems.util.list_node import ListNode
+
+
+class MergeTwoListsTest(unittest.TestCase):
+    def test_merge_two_lists(self):
+        list1 = ListNode(1, ListNode(3, ListNode(5)))
+        list2 = ListNode(2, ListNode(4, ListNode(6)))
+        merged_list = MergeTwoSortedLists.mergeTwoLists(list1, list2)
+
+        self.assertEqual(merged_list.val, 1)
+        self.assertEqual(merged_list.next.val, 2)
+        self.assertEqual(merged_list.next.next.val, 3)
+        self.assertEqual(merged_list.next.next.next.val, 4)
+        self.assertEqual(merged_list.next.next.next.next.val, 5)
+        self.assertEqual(merged_list.next.next.next.next.next.val, 6)
+
+    def test_merge_with_null_list(self):
+        list1 = None
+        list2 = ListNode(1, ListNode(2, ListNode(3)))
+        merged_list = MergeTwoSortedLists.mergeTwoLists(list1, list2)
+
+        self.assertEqual(merged_list.val, 1)
+        self.assertEqual(merged_list.next.val, 2)
+        self.assertEqual(merged_list.next.next.val, 3)
+
+    def test_merge_both_null(self):
+        list1 = None
+        list2 = None
+        merged_list = MergeTwoSortedLists.mergeTwoLists(list1, list2)
+        self.assertIsNone(merged_list)
+
+
+if __name__ == '__main__':
+    unittest.main()