24. Swap Nodes in Pairs.

    - Language: Python.
    - Time complexity: O(n).
    - Space complexity: O(1).
    - Method: Swapping node using pointers.

Author: welder87

python_solutions/lc_24_swap_nodes_in_pairs/lc_24_swap_nodes_in_pairs.py

@@ -6,6 +6,7 @@
 class Solution:
     def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
         # Time complexity: O(n). Space complexity: O(1).
+        # Method: Data Overwriting.
         if head is None:
             return head
         left, right = head, head.next
@@ -16,3 +17,17 @@ def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
                 break
             right = left.next
         return head
+
+    def swapPairsV1(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        # Time complexity: O(n). Space complexity: O(1).
+        # Method: Swapping node using pointers.
+        dummy = ListNode(val=-1, next=head)
+        prev, head = dummy, head
+        while head is not None and head.next is not None:
+            nxt = head.next
+            prev.next = nxt
+            head.next = nxt.next
+            nxt.next = head
+            prev = head
+            head = head.next
+        return dummy.next

python_solutions/lc_24_swap_nodes_in_pairs/test_lc_24_swap_nodes_in_pairs.py

@@ -28,6 +28,13 @@ def test_success_v0(lst: list[int], ans: list[int], solution: Solution):
     assert compare_singly_linked_lists(res, to_singly_linked_list(ans))
 
 
+@pytest.mark.parametrize(("lst", "ans"), test_cases)
+def test_success_v1(lst: list[int], ans: list[int], solution: Solution):
+    res = solution.swapPairsV1(to_singly_linked_list(lst))
+    assert to_list(res) == ans
+    assert compare_singly_linked_lists(res, to_singly_linked_list(ans))
+
+
 @pytest.fixture
 def solution() -> Solution:
     return Solution()