add reverse k group linkedlist

data_structures/linked_list/reverse_k_group.py

@@ -0,0 +1,124 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Node:
+    data: int
+    next_node: Node | None = None
+
+
+def insert_node(head: Node | None, data: int) -> Node:
+    """
+    Insert a new node at the end of a linked list and return the new head.
+    >>> head = insert_node(None, 1)
+    >>> head = insert_node(head, 2)
+    >>> head = insert_node(head, 3)
+    >>> print_linked_list(head)
+    1->2->3
+    """
+    new_node = Node(data)
+    # If the linked list is empty, the new_node becomes the head
+    if head is None:
+        return new_node
+
+    temp_node = head
+    while temp_node.next_node is not None:
+        temp_node = temp_node.next_node
+
+    temp_node.next_node = new_node  # type: ignore
+    return head
+
+
+def length_of_linked_list(head: Node | None) -> int:
+    """
+    find length of linked list
+    >>> head = insert_node(None, 10)
+    >>> head = insert_node(head, 9)
+    >>> head = insert_node(head, 8)
+    >>> length_of_linked_list(head)
+    3
+    """
+    length = 0
+    while head is not None:
+        length += 1
+        head = head.next_node
+    return length
+
+
+def print_linked_list(head: Node | None) -> None:
+    """
+    print the entire linked list
+    >>> head = insert_node(None, 1)
+    >>> head = insert_node(head, 2)
+    >>> head = insert_node(head, 3)
+    >>> print_linked_list(head)
+    1->2->3
+    """
+    if head is not None:
+        while head.next_node is not None:
+            print(head.data, end="->")
+            head = head.next_node
+        print(head.data)
+
+
+def reverse_k_nodes(head: Node | None, group_size: int) -> Node | None:
+    """
+    reverse nodes within groups of size k
+    >>> head = insert_node(None, 1)
+    >>> head = insert_node(head, 2)
+    >>> head = insert_node(head, 3)
+    >>> head = insert_node(head, 4)
+    >>> head = insert_node(head, 5)
+    >>> new_head = reverse_k_nodes(head, 2)
+    >>> print_linked_list(new_head)
+    2->1->4->3->5
+    """
+    if head is None or head.next_node is None:
+        return head
+
+    length = length_of_linked_list(head)
+
+    dummy_head = Node(0)
+    dummy_head.next_node = head
+
+    previous_node = dummy_head
+
+    while length >= group_size:
+        assert previous_node
+        current_node = previous_node.next_node
+        assert current_node
+        next_node = current_node.next_node
+        for _ in range(1, group_size):
+            assert next_node, current_node
+            current_node.next_node = next_node.next_node
+            assert previous_node
+            next_node.next_node = previous_node.next_node
+            assert previous_node
+            previous_node.next_node = next_node
+            assert current_node
+            next_node = current_node.next_node
+        previous_node = current_node
+        length -= group_size
+    assert dummy_head
+    return dummy_head.next_node
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+
+    k = 2
+    head = insert_node(None, 1)
+    head = insert_node(head, 2)
+    head = insert_node(head, 3)
+    head = insert_node(head, 4)
+    head = insert_node(head, 5)
+
+    print("Original Linked List: ", end="")
+    print_linked_list(head)
+    print(f"After reversing groups of size {k}: ", end="")
+    new_head = reverse_k_nodes(head, k)
+    print_linked_list(new_head)