diff --git a/data_structures/linked_list/rotate_to_the_right.py b/data_structures/linked_list/rotate_to_the_right.py new file mode 100644 index 000000000..51b10481c --- /dev/null +++ b/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)