Module dsa.doublylinkedlist

Module containing doubly linked list class.

Classes

class DoublyLinkedList (head=None, tail=None, count=0)

A doubly linked list implementation.

Initialize a singly linked list.

if only the head node is specified, tail is set to the head node and count is automatically set to 0 if both head and tail nodes are specified, count should be specified as well

Args

head
reference to the head node
tail
reference to the tail node
count
the number of nodes in the linked list
Expand source code
class DoublyLinkedList:
    """ 
    A doubly linked list implementation.
    """
    def __init__(self, head=None, tail=None, count=0):
        """ 
        Initialize a singly linked list.
        
        if only the head node is specified, tail is set to the head node and count is automatically set to 0
        if both head and tail nodes are specified, count should be specified as well
        
        Args:
            head: reference to the head node
            tail: reference to the tail node
            count: the number of nodes in the linked list

        """        
        self.head = head
        if head and tail is None:
            self.tail = head
            self.count = 1
        else:
            self.tail = tail
            self.count = count

    @classmethod
    def from_list(cls, mylist=None):
        """
        Create a linked list from a list.

        Args:
            mylist: a list or container to convert from
        
        Returns:
            Linked List
        """
        ll = cls()
        for value in mylist:
            ll.append(value)

        return ll
    
    def to_list(self) -> list:
        """
        Create a list with contents of the linked list.

        Returns:
            list with contents of linked list
        """
        mylist = []
        current = self.head
        while current:
            mylist.append(current.value)
            current = current.next
        return mylist
        
    def __repr__(self):
        s = ""
        current = self.head
        while current:
            s += str(current.value) + " "
            current = current.next

        return f"[ {s}] Count: {self.count}"

    def __getitem__(self, index: int) -> Node:
        """ 
        Return value at a specified index. Raise exception if index is out of bounds.
        
        Args:
            index: index of value
        """        
        i = 0
        current = self.head
        while current:
            if i == index:
                return current.value
            current = current.next
            i += 1
        raise IndexError("Index Out of Bounds")
    
    def __len__(self) -> int:
        return self.count
    
    def is_empty(self) -> bool:
        return self.count == 0

    def print(self):
        """
        Print the contents of the linked list.
        """
        current = self.head
        while current:
            print(current.value, end=" ")
            current = current.next
        print()

    def print_reverse(self):
        """
        Print the contents of the linked list in reverse order.
        """
        current = self.tail
        while current:
            print(current.value, end=" ")
            current = current.prev
        print()
    
    def search(self, value) -> int:
        """
        Search for a value in the linked list. Raise exception if value is not found.

        Args:
            value: value to search for

        Returns:
            return index of found value
        """
        i = 0
        current = self.head
        while current:
            if current.value == value:
                return i
            i += 1
            current = current.next
        raise Exception("Value not found")
    
    def insert(self, index: int, value):
        """
        Insert a value at a specified index. Raise exception if index is out of bounds.

        Args:
            index: the index to insert a value
            value: a value to append
        """
        
        # insert front
        if index == 0:
            self.prepend(value)
            return
            
        # find node to insert after
        i = 0
        current = self.head
        while index < i or current:
            if i == index:
                break
            current = current.next
            i += 1

        if index > i:
            raise IndexError("Index Out of Bounds")

        new_node = Node(value)
        new_node.next = current
        new_node.prev = current.prev
        current.prev = new_node
        new_node.prev.next = new_node

        self.count += 1
        
    def prepend(self, value):
        """
        Place a value at the beginning of the linked list.

        Args:
            value: a value to append
        """
        new_node = Node(value)
        new_node.next = self.head
        self.head.prev = new_node
        self.head = new_node
        self.count += 1

    def append(self, value):
        """
        Place a value at the end of the linked list.

        Args:
            value: a value to append
        """
        if self.head is None:
            self.head = Node(value)
            if self.count == 0:
                self.tail = self.head
            self.count += 1
            return
        
        # go to the end of the list
        new_node = Node(value)
        new_node.prev = self.tail
        self.tail.next = new_node
        self.tail = new_node
        
        self.count += 1
        

    def delete(self, index):
        """
        Delete a node at a specified index. Raise Exception if linked list is empty or if index is not found.

        Args:
            index: index of element to be deleted
        """
        if self.head is None:
            raise IndexError("DoublyLinkedList is Empty")

        i = 0
        if index == 0:
            self.head = self.head.next
            if self.head:
                self.head.prev = None
            self.count -= 1
            return
        
        current = self.head
        while current:
            if index == i:
                current.prev.next = current.next
                if current.next:
                    current.next.prev = current.prev
                else:
                    self.tail = current.prev

                self.count -= 1
                return
            current = current.next
            i += 1
        raise IndexError("Index not found")

Static methods

def from_list(mylist=None)

Create a linked list from a list.

Args

mylist
a list or container to convert from

Returns

Linked List

Methods

def append(self, value)

Place a value at the end of the linked list.

Args

value
a value to append
def delete(self, index)

Delete a node at a specified index. Raise Exception if linked list is empty or if index is not found.

Args

index
index of element to be deleted
def insert(self, index: int, value)

Insert a value at a specified index. Raise exception if index is out of bounds.

Args

index
the index to insert a value
value
a value to append
def is_empty(self) ‑> bool
def prepend(self, value)

Place a value at the beginning of the linked list.

Args

value
a value to append
def print(self)

Print the contents of the linked list.

def print_reverse(self)

Print the contents of the linked list in reverse order.

def search(self, value) ‑> int

Search for a value in the linked list. Raise exception if value is not found.

Args

value
value to search for

Returns

return index of found value

def to_list(self) ‑> list

Create a list with contents of the linked list.

Returns

list with contents of linked list

class Node (value)

A doubly linked list node implementation.

Args

value
the value of the node
Expand source code
class Node:
    """ 
    A doubly linked list node implementation.
    """
    def __init__(self, value):
        """ 
        Args:
            value: the value of the node
        """
        #: value of the node
        self.value = value
        #: reference to the next node
        self.next = None
        #: reference to the previous node
        self.prev = None

Instance variables

var next

reference to the next node

var prev

reference to the previous node

var value

value of the node