Add problem 25 - Reverse Nodes In K Group

Author: anirudhology

problems/linked_list/reverse_nodes_in_k_group.py

@@ -0,0 +1,39 @@
+from typing import Optional
+
+from problems.util.list_node import ListNode
+
+
+class ReverseNodesInKGroup:
+    @staticmethod
+    def reverseKGroup(head: Optional[ListNode], k: int) -> Optional[ListNode]:
+        # Special case
+        if head is None or k <= 0:
+            return head
+        # Dummy head
+        dummy = ListNode()
+        dummy.next = head
+        # Pointer to traverse the list
+        temp = dummy
+        # Traverse the list
+        while True:
+            current_temp = temp
+            # Check if we have k nodes to reverse
+            index = 0
+            while index < k and current_temp is not None:
+                current_temp = current_temp.next
+                index += 1
+            if current_temp is None:
+                break
+            # Reverse the list
+            previous_node, current_node, next_node = None, temp.next, None
+            for i in range(k):
+                next_node = current_node.next
+                current_node.next = previous_node
+                previous_node = current_node
+                current_node = next_node
+            # Tail of the group
+            tail = temp.next
+            tail.next = current_node
+            temp.next = previous_node
+            temp = tail
+        return dummy.next

tests/linked_list/reverse_nodes_in_k_groups_test.py

@@ -0,0 +1,63 @@
+import unittest
+
+from problems.linked_list.reverse_nodes_in_k_group import ReverseNodesInKGroup
+from problems.util.list_node import ListNode
+
+
+class ReverseNodesInKGroupTest(unittest.TestCase):
+
+    @staticmethod
+    def create_list(values):
+        dummy = ListNode()
+        current = dummy
+        for value in values:
+            current.next = ListNode(value)
+            current = current.next
+        return dummy.next
+
+    @staticmethod
+    def list_to_array(head):
+        result = []
+        current = head
+        while current is not None:
+            result.append(current.val)
+            current = current.next
+        return result
+
+    def test_reverseKGroup_with_null_head(self):
+        result = ReverseNodesInKGroup.reverseKGroup(None, 3)
+        self.assertIsNone(result)
+
+    def test_reverseKGroup_with_k_less_than_or_equal_to_zero(self):
+        head = self.create_list([1, 2, 3])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 0)
+        self.assertEqual(self.list_to_array(result), [1, 2, 3])
+
+    def test_reverseKGroup_with_single_element(self):
+        head = self.create_list([1])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 1)
+        self.assertEqual(self.list_to_array(result), [1])
+
+    def test_reverseKGroup_with_k_greater_than_list_length(self):
+        head = self.create_list([1, 2, 3])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 4)
+        self.assertEqual(self.list_to_array(result), [1, 2, 3])
+
+    def test_reverseKGroup_with_k_equals_list_length(self):
+        head = self.create_list([1, 2, 3])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 3)
+        self.assertEqual(self.list_to_array(result), [3, 2, 1])
+
+    def test_reverseKGroup_with_multiple_k_groups(self):
+        head = self.create_list([1, 2, 3, 4, 5])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 2)
+        self.assertEqual(self.list_to_array(result), [2, 1, 4, 3, 5])
+
+    def test_reverseKGroup_with_remaining_nodes_less_than_k(self):
+        head = self.create_list([1, 2, 3, 4, 5])
+        result = ReverseNodesInKGroup.reverseKGroup(head, 3)
+        self.assertEqual(self.list_to_array(result), [3, 2, 1, 4, 5])
+
+
+if __name__ == '__main__':
+    unittest.main()