LinkedList.py

from typing import Any
from Node import Node


class LinkedList:
    def __init__(self):
        """
        Create and initialize LinkedList class instance.
        >>> linked_list = LinkedList()
        """
        self.head = None

    def __iter__(self) -> Any:
        """
        This function is intended for iterators to access
        and iterate through data inside linked list.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("tail")
        >>> linked_list.insert_tail("tail_1")
        >>> linked_list.insert_tail("tail_2")
        >>> for node in linked_list: # __iter__ used here.
        ...     node
        'tail'
        'tail_1'
        'tail_2'
        """
        node = self.head
        while node:
            yield node.data
            node = node.next

    def __len__(self) -> int:
        """
        Return length of linked list (number of nodes)
        >>> linked_list = LinkedList()
        >>> len(linked_list)
        0
        >>> linked_list.insert_tail("tail")
        >>> len(linked_list)
        1
        >>> linked_list.insert_head("head")
        >>> len(linked_list)
        2
        >>> _ = linked_list.delete_tail()
        >>> len(linked_list)
        1
        >>> _ = linked_list.delete_head()
        >>> len(linked_list)
        0
        """
        return len(tuple(iter(self)))

    def __repr__(self) -> str:
        """
        String representation/visualization of a Linked List
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail(1)
        >>> linked_list.insert_tail(3)
        >>> linked_list.__repr__()
        '1->3'
        """
        return "->".join([str(item) for item in self])

    def __getitem__(self, index: int) -> Any:
        """
        Indexing Support. Used to get a node at particular position
        >>> linked_list = LinkedList()
        >>> for i in range(0, 10):
        ...     linked_list.insert_nth(i, i)
        >>> all(str(linked_list[i]) == str(i) for i in range(0, 10))
        True
        >>> linked_list[-10]
        Traceback (most recent call last):
        ...
        ValueError: list index out of range.
        >>> linked_list[len(linked_list)]
        Traceback (most recent call last):
        ...
        ValueError: list index out of range.
        """
        if not 0 <= index < len(self):
            raise ValueError("list index out of range.")
        for i, node in enumerate(self):
            if i == index:
                return node

    def __setitem__(self, index: int, data: Any) -> None:
        """
        Insertion Support. Used to change the data of a particular node
        >>> linked_list = LinkedList()
        >>> for i in range(0, 10):
        ...     linked_list.insert_nth(i, i)
        >>> linked_list[0] = 666
        >>> linked_list[0]
        666
        >>> linked_list[5] = -666
        >>> linked_list[5]
        -666
        >>> linked_list[-10] = 666
        Traceback (most recent call last):
        ...
        ValueError: list index out of range.
        >>> linked_list[len(linked_list)] = 666
        Traceback (most recent call last):
        ...
        ValueError: list index out of range.
        """
        if not 0 <= index < len(self):
            raise ValueError("list index out of range.")
        current = self.head
        for i in range(index):
            current = current.next
        current.data = data

    def __add__(self, linked_list) -> Any:
        """
        Merge two linked lists together.
        >>> linked_list = LinkedList()
        >>> linked_list2 = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list2.insert_tail("one")
        >>> linked_list2.insert_tail("two")
        >>> merged = linked_list + linked_list2
        >>> print(merged)
        first->second->one->two
        """
        for node in linked_list:
            self.insert_tail(node)
        return self

    def insert_tail(self, data: Any) -> None:
        """
        Insert data to the end of linked list.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("tail")
        >>> linked_list
        tail
        >>> linked_list.insert_tail("tail_2")
        >>> linked_list
        tail->tail_2
        >>> linked_list.insert_tail("tail_3")
        >>> linked_list
        tail->tail_2->tail_3
        """
        self.insert_nth(len(self), data)

    def insert_head(self, data: Any) -> None:
        """
        Insert data to the beginning of linked list.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_head("head")
        >>> linked_list
        head
        >>> linked_list.insert_head("head_2")
        >>> linked_list
        head_2->head
        >>> linked_list.insert_head("head_3")
        >>> linked_list
        head_3->head_2->head
        """
        self.insert_nth(0, data)

    def insert_nth(self, index: int, data: Any) -> None:
        """
        Insert data at given index.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        >>> linked_list.insert_nth(1, "fourth")
        >>> linked_list
        first->fourth->second->third
        >>> linked_list.insert_nth(3, "fifth")
        >>> linked_list
        first->fourth->second->fifth->third
        """
        if not 0 <= index <= len(self):
            raise IndexError("list index out of range")
        new_node = Node(data)
        if self.head is None:
            self.head = new_node
        elif index == 0:
            new_node.next = self.head  # link new_node to head
            self.head = new_node
        else:
            temp = self.head
            for _ in range(index - 1):
                temp = temp.next
            new_node.next = temp.next
            temp.next = new_node

    def print_list(self) -> None:  # print every node data
        """
        This method prints every node data.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        """
        print(self)

    def delete_head(self) -> Any:
        """
        Delete the first node and return the
        node's data.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        >>> linked_list.delete_head()
        'first'
        >>> linked_list
        second->third
        >>> linked_list.delete_head()
        'second'
        >>> linked_list
        third
        >>> linked_list.delete_head()
        'third'
        >>> linked_list.delete_head()
        Traceback (most recent call last):
        ...
        IndexError: List index out of range.
        """
        return self.delete_nth(0)

    def delete_tail(self) -> Any:  # delete from tail
        """
        Delete the tail end node and return the
        node's data.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        >>> linked_list.delete_tail()
        'third'
        >>> linked_list
        first->second
        >>> linked_list.delete_tail()
        'second'
        >>> linked_list
        first
        >>> linked_list.delete_tail()
        'first'
        >>> linked_list.delete_tail()
        Traceback (most recent call last):
        ...
        IndexError: List index out of range.
        """
        return self.delete_nth(len(self) - 1)

    def delete_nth(self, index: int = 0) -> Any:
        """
        Delete node at given index and return the
        node's data.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        >>> linked_list.delete_nth(1) # delete middle
        'second'
        >>> linked_list
        first->third
        >>> linked_list.delete_nth(5) # this raises error
        Traceback (most recent call last):
        ...
        IndexError: List index out of range.
        >>> linked_list.delete_nth(-1) # this also raises error
        Traceback (most recent call last):
        ...
        IndexError: List index out of range.
        """
        if not 0 <= index <= len(self) - 1:  # test if index is valid
            raise IndexError("List index out of range.")
        delete_node = self.head  # default first node
        if index == 0:
            self.head = self.head.next
        else:
            temp = self.head
            for _ in range(index - 1):
                temp = temp.next
            delete_node = temp.next
            temp.next = temp.next.next
        return delete_node.data

    def is_empty(self) -> bool:
        """
        Check if linked list is empty.
        >>> linked_list = LinkedList()
        >>> linked_list.is_empty()
        True
        >>> linked_list.insert_head("first")
        >>> linked_list.is_empty()
        False
        """
        return self.head is None

    def reverse(self) -> None:
        """
        This reverses the linked list order.
        >>> linked_list = LinkedList()
        >>> linked_list.insert_tail("first")
        >>> linked_list.insert_tail("second")
        >>> linked_list.insert_tail("third")
        >>> linked_list
        first->second->third
        >>> linked_list.reverse()
        >>> linked_list
        third->second->first
        """
        prev = None
        current = self.head

        while current:
            # Store the current node's next node.
            next_node = current.next
            # Make the current node's next point backwards
            current.next = prev
            # Make the previous node be the current node
            prev = current
            # Make the current node the next node (to progress iteration)
            current = next_node
        # Return prev in order to put the head at the end
        self.head = prev


if __name__ == '__main__':
    from doctest import testmod
    testmod()