Module dsa.doublylinkedlist

Expand source code
class Node:
    """ 
    A doubly linked list node implementation in Python
    """
    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
    
class DoublyLinkedList:
    """ 
    A doubly linked list implementation in Python
    """
    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 is not None and tail is None:
            self.tail = head
            self.count = 1
        else:
            self.tail = tail
            self.count = count

    @classmethod
    def from_array(cls, mylist=None):
        ''' create a linked list from an array '''
        ll = cls()
        for value in mylist:
            ll.append(value)

        return ll
        
    def __repr__(self):
        s = ""
        current = self.head
        while current is not None:
            s += str(current.value) + " "
            current = current.next

        return f"[{s}] Count: {self.count}"
    
    def print(self):
        """
        Print the contents of the linked list.
        """
        current = self.head
        while current is not None:
            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 is not None:
            print(current.value, end=" ")
            current = current.prev
        print()
    
    def search(self, value) -> int:
        """
        Search for a value in the linked list.

        Args:
            value: value to search for

        Returns:
            return index of found value
        """
        i = 0
        current = self.head
        while current is not None:
            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.

        Args:
            index: the index to insert a value
            value: a value to append
        """
        
        # insert front
        if index == 0:
            self.prepend(value)
            return
            
        i = 0
        current = self.head
        while index < i or current is not None:
            if i == index:
                break
            current = current.next
            i += 1

        if index > i:
            raise Exception("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 Exception("DoublyLinkedList is Empty")

        i = 0
        if index == 0:
            self.head = self.head.next
            if self.head is not None:
                self.head.prev = None
            self.count -= 1
            return
        
        current = self.head
        while current is not None:
            if index == i:
                current.prev.next = current.next
                if current.next is not None:
                    current.next.prev = current.prev
                else:
                    self.tail = current.prev

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

Classes

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

A doubly linked list implementation in Python

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 in Python
    """
    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 is not None and tail is None:
            self.tail = head
            self.count = 1
        else:
            self.tail = tail
            self.count = count

    @classmethod
    def from_array(cls, mylist=None):
        ''' create a linked list from an array '''
        ll = cls()
        for value in mylist:
            ll.append(value)

        return ll
        
    def __repr__(self):
        s = ""
        current = self.head
        while current is not None:
            s += str(current.value) + " "
            current = current.next

        return f"[{s}] Count: {self.count}"
    
    def print(self):
        """
        Print the contents of the linked list.
        """
        current = self.head
        while current is not None:
            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 is not None:
            print(current.value, end=" ")
            current = current.prev
        print()
    
    def search(self, value) -> int:
        """
        Search for a value in the linked list.

        Args:
            value: value to search for

        Returns:
            return index of found value
        """
        i = 0
        current = self.head
        while current is not None:
            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.

        Args:
            index: the index to insert a value
            value: a value to append
        """
        
        # insert front
        if index == 0:
            self.prepend(value)
            return
            
        i = 0
        current = self.head
        while index < i or current is not None:
            if i == index:
                break
            current = current.next
            i += 1

        if index > i:
            raise Exception("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 Exception("DoublyLinkedList is Empty")

        i = 0
        if index == 0:
            self.head = self.head.next
            if self.head is not None:
                self.head.prev = None
            self.count -= 1
            return
        
        current = self.head
        while current is not None:
            if index == i:
                current.prev.next = current.next
                if current.next is not None:
                    current.next.prev = current.prev
                else:
                    self.tail = current.prev

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

Static methods

def from_array(mylist=None)

create a linked list from an array

Expand source code
@classmethod
def from_array(cls, mylist=None):
    ''' create a linked list from an array '''
    ll = cls()
    for value in mylist:
        ll.append(value)

    return ll

Methods

def append(self, value)

Place a value at the end of the linked list.

Args

value
a value to append
Expand source code
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
Expand source code
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 Exception("DoublyLinkedList is Empty")

    i = 0
    if index == 0:
        self.head = self.head.next
        if self.head is not None:
            self.head.prev = None
        self.count -= 1
        return
    
    current = self.head
    while current is not None:
        if index == i:
            current.prev.next = current.next
            if current.next is not None:
                current.next.prev = current.prev
            else:
                self.tail = current.prev

            self.count -= 1
            return
        current = current.next
        i += 1
    raise Exception("Index not found")
def insert(self, index: int, value)

Insert a value at a specified index.

Args

index
the index to insert a value
value
a value to append
Expand source code
def insert(self, index: int, value):
    """
    Insert a value at a specified index.

    Args:
        index: the index to insert a value
        value: a value to append
    """
    
    # insert front
    if index == 0:
        self.prepend(value)
        return
        
    i = 0
    current = self.head
    while index < i or current is not None:
        if i == index:
            break
        current = current.next
        i += 1

    if index > i:
        raise Exception("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
Expand source code
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 print(self)

Print the contents of the linked list.

Expand source code
def print(self):
    """
    Print the contents of the linked list.
    """
    current = self.head
    while current is not None:
        print(current.value, end=" ")
        current = current.next
    print()
def print_reverse(self)

Print the contents of the linked list in reverse order.

Expand source code
def print_reverse(self):
    """
    Print the contents of the linked list in reverse order.
    """
    current = self.tail
    while current is not None:
        print(current.value, end=" ")
        current = current.prev
    print()
def search(self, value) ‑> int

Search for a value in the linked list.

Args

value
value to search for

Returns

return index of found value

Expand source code
def search(self, value) -> int:
    """
    Search for a value in the linked list.

    Args:
        value: value to search for

    Returns:
        return index of found value
    """
    i = 0
    current = self.head
    while current is not None:
        if current.value == value:
            return i
        i += 1
        current = current.next
    raise Exception("Value not found")
class Node (value)

A doubly linked list node implementation in Python

Args

value
the value of the node
Expand source code
class Node:
    """ 
    A doubly linked list node implementation in Python
    """
    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