Deletion in Doubly linked list - Data structures and algorithms

In this tutorial, we are going to learn how to perform deletion operations in the doubly linked list.

after completing this tutorial you are able to learn how to

1. Delete the first node.
2. Delete the only node.
3. Delete a node in between the nodes.
4. Delete the last node.

Deletion of the first node from the doubly linked list.

as you see we have a doubly-linked list that has four nodes. so after deleting the first node second node become the first node.


so first we store the second node's reference to the start variable.


and then we set the second node's previous link part to Null or None. because the previous link part of the first node in the doubly linked list is always None or Null.


so after performing these steps, the first node is deleted.

Delete the only node from the doubly linked list.

if a linked list has only one node then to delete this node we set the start variable to the None.




so now our list becomes an empty list.

Delete a node in between the nodes.

to delete a node between two nodes first we need to find out reference to the node that we want to delete. as you see to delete the third node first we found a reference p to that node.


and then we store the reference of the node that comes after node p into the next link part of the node that comes before the node p.


and then we store the reference of the node that comes before node p into the previous link part of the node that comes after node p.


now after performing these steps now, the third node has deleted from the doubly linked list.

Delete the last node from the doubly linked list.

to delete the last node of the list first we need to find out the reference of the last node.


and then we set the next link part of the node to Null or None that come before node p.


so after performing these steps now the last node of the list is deleted.

Python code to delete the node in the Doubly linked list

class Node(object):

    def __init__(self, value):
        self.info = value
        self.prev = None        self.next = None

class DoubleLinkedList(object):

    def __init__(self):
        self.start = None
    def display_list(self):
        if self.start is None:
            print("LIst is empty")
            return
        print("List is : ")
        p = self.start
        while p is not None:
            print(p.info, " ", end='')
            p = p.next
        print()

    def insert_in_beginning(self, data):
        temp = None(data)
        temp.next = self.start
        self.start.prev = temp
        self.start = temp

    def insert_in_empty_list(self, data):
        temp = Node(data)
        self.start = temp

    def insert_at_end(self, data):
        temp = Node(data)
        p = self.start
        while p.next is not None:
            p = p.next
        p.next = temp
        temp.prev = p

    def create_list(self):
        n = int(input("Enter the number of nodes : "))
        if n == 0:
            return        data = int(input("Enter the first element to be inserted : "))
        self.insert_in_empty_list(data)

        for i in range(n - 1):
            data = int(input("Enter the next element to be inserted : "))
            self.insert_at_end(data)

    def insert_after(self, data, x):
        temp = Node(data)
        p = self.start
        while p is not None:
            if p.info == x:
                break            p = p.next

        if p is None:
            print(x, " not present in the list")
        else:
            temp.prev = p
            temp.next = p.next
            if p.next is not None:
                p.next.prev = temp
            p.next = temp

    def insert_before(self, data, x):
        if self.start is None:
            print("List is empty")
            return
        if self.start.info == x:
            temp = Node(data)
            temp.next = self.start
            self.start.prev = temp
            self.start = temp
            return
        p = self.start
        while p is not None:
            if p.info == x:
                break            p = p.next

        if p is None:
            print(x, " not present in the list")
        else:
            temp = Node(data)
            temp.prev = p.prev
            temp.next = p
            p.prev.next = temp
            p.prev = temp

    def delete_first_node(self):
        if self.start is None:
            return        if self.start.next is None:
            self.start = None            return        self.start = self.start.next
        self.start.prev = None
    def delete_last_node(self):
        if self.start is None:
            return        if self.start.next is None:
            self.start = None            return
        p = self.start
        while p.next != None:
            p = p.next
        p.prev.next = None
    def delete_node(self, x):
        if self.start is None:
            return        if self.start.next is None:
            if self.start.info == x:
                self.start = None            else:
                print(x, " not found")
            return
        if self.start.info == x:
            self.start = self.start.next
            self.start.prev = None            return
        p = self.start.next
        while p.next is not None:
            if p.info == x:
                break
            p = p.next

        if p.next is not None:
            p.prev.next = p.next
            p.next.prev = p.prev
        else:
            if p.info == x:
                p.prev.next
            else:
                print(x, " not found")

    def reverse_list(self):
        if self.start is None:
            return
        p1 = self.start
        p2 = p1.next
        p1.next = None        p1.prev = p2
        while p2 is not None:
            p2.prev = p2.next
            p2.next = p1
            p1 = p2
            p2 = p2.prev
        self.start = p1


#################################################################3
list = DoubleLinkedList()

list.create_list()

while True:
    print("1. Display list")
    print("2. Insert in empty list")
    print("3. Insert a node in the beginning of the list")
    print("4. Insert a node at the end of the list")
    print("5. Insert a node after a specified node")
    print("6. Insert a node before a specified node")
    print("7. Delete first node")
    print("8. Delete last node")
    print("9. Delete any node")
    print("10. Reverse the list")
    print("11. Quit")

    option = int(input("Enter your choice : "))

    if option == 1:
        list.display_list()
    elif option == 2:
        data = int(input("Enter the element to be inserted : "))
        list.insert_in_empty_list(data)
    elif option == 3:
        data = int(input("Enter the element to be inserted : "))
        list.insert_in_beginning(data)
    elif option == 4:
        data = int(input("Enter the element to be inserted : "))
        list.insert_at_end(data)
    elif option == 5:
        data = int(input("Enter the element to be inserted : "))
        x = int(input("Enter the element after which to insert : "))
        list.insert_after(data, x)
    elif option == 6:
        data = int(input("Enter the element to be inserted : "))
        x = int(input("Enter the element before which to inserted : "))
        list.insert_before(data, x)
    elif option == 7:
        list.delete_first_node()
    elif option == 8:
        list.delete_last_node()
    elif option == 9:
        data = int(input("Enter the element to be deleted : "))
        list.delete_node(data)
    elif option == 10:
        list.reverse_list()
    elif option == 11:
        break    else:
        print("Wrong option")
    print()