[NEW ALGORITHM] Rotate linked list by K.

data_structures/linked_list/rotate_to_the_right.py

@@ -0,0 +1,156 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Node:
+    data: int
+    next_node: Node | None = None
+
+
+def print_linked_list(head: Node | None) -> None:
+    """
+        Print the entire linked list iteratively.
+
+        This function prints the elements of a linked list separated by '->'.
+
+        Parameters:
+            head (Node | None): The head of the linked list to be printed,
+    or None if the linked list is empty.
+
+        >>> head = insert_node(None, 0)
+        >>> head = insert_node(head, 2)
+        >>> head = insert_node(head, 1)
+        >>> print_linked_list(head)
+        0->2->1
+        >>> head = insert_node(head, 4)
+        >>> head = insert_node(head, 5)
+        >>> print_linked_list(head)
+        0->2->1->4->5
+    """
+    if head is None:
+        return
+    while head.next_node is not None:
+        print(head.data, end="->")
+        head = head.next_node
+    print(head.data)
+
+
+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.
+
+    Parameters:
+        head (Node | None): The head of the linked list.
+        data (int): The data to be inserted into the new node.
+
+    Returns:
+        Node: The new head of the linked list.
+
+    >>> head = insert_node(None, 10)
+    >>> head = insert_node(head, 9)
+    >>> head = insert_node(head, 8)
+    >>> print_linked_list(head)
+    10->9->8
+    """
+    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:
+        temp_node = temp_node.next_node
+
+    temp_node.next_node = new_node  # type: ignore
+    return head
+
+
+def rotate_to_the_right(head: Node, places: int) -> Node:
+    """
+    Rotate a linked list to the right by places times.
+
+    Parameters:
+        head: The head of the linked list.
+        places: The number of places to rotate.
+
+    Returns:
+        Node: The head of the rotated linked list.
+
+    >>> rotate_to_the_right(None, places=1)
+    Traceback (most recent call last):
+        ...
+    ValueError: The linked list is empty.
+    >>> head = insert_node(None, 1)
+    >>> rotate_to_the_right(head, places=1) == head
+    True
+    >>> 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 = rotate_to_the_right(head, places=2)
+    >>> print_linked_list(new_head)
+    4->5->1->2->3
+    """
+    # Check if the list is empty or has only one element
+    if not head:
+        raise ValueError("The linked list is empty.")
+
+    if head.next_node is None:
+        return head
+
+    # Calculate the length of the linked list
+    length = 1
+    temp_node = head
+    while temp_node.next_node is not None:
+        length += 1
+        temp_node = temp_node.next_node
+
+    # Adjust the value of places to avoid places longer than the list.
+    places %= length
+
+    if places == 0:
+        return head  # As no rotation is needed.
+
+    # Find the new head position after rotation.
+    new_head_index = length - places
+
+    # Traverse to the new head position
+    temp_node = head
+    for _ in range(new_head_index - 1):
+        assert temp_node.next_node
+        temp_node = temp_node.next_node
+
+    # Update pointers to perform rotation
+    assert temp_node.next_node
+    new_head = temp_node.next_node
+    temp_node.next_node = None
+    temp_node = new_head
+    while temp_node.next_node:
+        temp_node = temp_node.next_node
+    temp_node.next_node = head
+
+    assert new_head
+    return new_head
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    head = insert_node(None, 5)
+    head = insert_node(head, 1)
+    head = insert_node(head, 2)
+    head = insert_node(head, 4)
+    head = insert_node(head, 3)
+
+    print("Original list: ", end="")
+    print_linked_list(head)
+
+    places = 3
+    new_head = rotate_to_the_right(head, places)
+
+    print(f"After {places} iterations: ", end="")
+    print_linked_list(new_head)