solve "61. Rotate List"

src/rotate_list.py

@@ -0,0 +1,40 @@
+from src.utils.linked_list import ListNode
+
+
+def get_length(head: ListNode | None) -> int:
+    result = 0
+
+    while head:
+        result += 1
+        head = head.next
+
+    return result
+
+
+class Solution:
+    def rotateRight(self, head: ListNode | None, k: int) -> ListNode | None:
+        n = get_length(head)
+
+        if n == 0 or n == 1:
+            return head
+
+        k = k % n
+        if k == 0:
+            return head
+
+        dummy = left = ListNode(next=head)
+
+        for _ in range(n - k):
+            assert left.next
+            left = left.next
+
+        new_start = left.next
+
+        last = left
+        while last and last.next:
+            last = last.next
+
+        dummy.next = new_start
+        last.next = head
+        left.next = None
+        return dummy.next

tests/test_rotate_list.py

@@ -0,0 +1,24 @@
+import pytest
+
+from src.rotate_list import Solution
+from src.utils.linked_list import to_linked_list
+from src.utils.linked_list import to_list
+
+
+@pytest.mark.parametrize(
+    "in_list,k,expected_out_list",
+    (
+        ([1, 2, 3, 4, 5], 2, [4, 5, 1, 2, 3]),
+        ([0, 1, 2], 4, [2, 0, 1]),
+        ([], 0, []),
+        ([], 1, []),
+        ([1], 1, [1]),
+        ([1, 2], 2, [1, 2]),
+        ([1], 99, [1]),
+    ),
+)
+def test_solution(in_list, k, expected_out_list):
+    head = to_linked_list(in_list)
+    out_head = Solution().rotateRight(head, k)
+    out_list = to_list(out_head)
+    assert out_list == expected_out_list