[NEW ALGORITHM] Rotate linked list by K.

data_structures/linked_list/rotate_linked_list_by_k.py

@@ -0,0 +1,144 @@
+from __future__ import annotations
+
+
+class Node:
+    def __init__(self, data: int) -> None:
+        self.data = data
+        self.next = None
+
+
+def print_linked_list(head: Node) -> None:
+    """
+    Print the entire linked list iteratively.
+
+    Parameters:
+        head (Node): The head of the linked list to be printed.
+
+    >>> head = None
+    >>> head = insert_node(head, 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 is not None:
+        print(head.data, end="->")
+        head = head.next
+    print(head.data)
+
+
+def insert_node(head: Node, data: int) -> Node:
+    """
+    Insert a new node at the end of a linked list and return the new head.
+
+    Parameters:
+        head (Node): 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 = None
+    >>> head = insert_node(head, 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 is not None:
+        temp_node = temp_node.next
+
+    temp_node.next = new_node
+    return head
+
+
+def right_rotate_by_k(head: Node, k: int) -> Node:
+    """
+    Rotate a linked list to the right by k times.
+
+    Parameters:
+        head (Node): The head of the linked list.
+        k (int): The number of places to rotate.
+
+    Returns:
+        Node: The head of the rotated linked list.
+
+    >>> head = None
+    >>> head = insert_node(head, 1)
+    >>> head = insert_node(head, 2)
+    >>> head = insert_node(head, 3)
+    >>> head = insert_node(head, 4)
+    >>> head = insert_node(head, 5)
+    >>> k = 2
+    >>> new_head = right_rotate_by_k(head, k)
+    >>> print_linked_list(new_head)
+    4->5->1->2->3
+    """
+    # Check if the list is empty or has only one element
+    if head is None or head.next is None:
+        return head
+
+    # Calculate the length of the linked list
+    length = 1
+    temp_node = head
+    while temp_node.next is not None:
+        length += 1
+        temp_node = temp_node.next
+
+    # Adjust the value of k to avoid unnecessary rotations.
+    k = k % length
+
+    if k == 0:
+        return head  # As No rotation needed.
+
+    # Find the new head position after rotation.
+    new_head_index = length - k
+
+    # Traverse to the new head position
+    temp_node = head
+    for _ in range(new_head_index - 1):
+        temp_node = temp_node.next
+
+    # Update pointers to perform rotation
+    new_head = temp_node.next
+    temp_node.next = None
+    temp_node = new_head
+    while temp_node.next is not None:
+        temp_node = temp_node.next
+    temp_node.next = head
+
+    return new_head
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    head = None
+
+    # head = insert_node(head, 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)
+
+    k = 3
+    new_head = right_rotate_by_k(head, k)
+
+    print("After", k, "iterations: ", end="")
+    print_linked_list(new_head)