Insertion in Dobly linked list - Data structures and algorithms

Insertion in a doubly-linked list: as we know in the node of the doubly linked list we have two link parts and one info part. and every node holds the reference of the previous and next node.

so to insert the new node at any position like at the first position, the last position, in between the nodes and before and after the node we need to maintain both references.

so after completing this tutorial, you will be able to learn about
  1. Insert node at the beginning of the linked list
  2. Insert node in an empty list.
  3. Insert node at the end of the list.
  4. Insert node after a node.
  5. Insert node before a node.

Inserting a node at the beginning of the doubly linked list.

to insert a node at the beginning of the list first we allocate a new node called temp. as you see in the image given below.

insertion in doubly linked list

after that, we store the first node's reference in the temp node's next link part.

insertion in doubly linked list

and then we store the new node temp's reference in the first node of the list. as you see in the image given below.

insertion in doubly linked list

after performing these steps we inserted a new node at the beginning of the list.

Insert a node in an empty doubly-linked list.

as we know we don't have any node in an empty list. 

insertion in doubly linked list

so to insert a node in an empty list first we allocate a new node called temp and store the reference of the new node in the start variable.

insertion in doubly linked list


Insert a node at the end of the doubly linked list.

to insert a new node at the end of the list first we need a reference of the last node of the doubly linked list. so we find a reference for the last node called p.

insertion in doubly linked list

after that, we allocate a new node called temp.

insertion in doubly linked list

and then we store the new node's reference in the next link part of the node p.

insertion in doubly linked list

and then we store the p node's reference into the new node's previous link part.

insertion in doubly linked list

after performing these steps we now inserted a new node at the end of the list.


Insert a node after a node in the doubly linked list.

like if we want to insert a node after a node called p.

insertion in doubly linked list

then we first allocate a new node called temp.

insertion in doubly linked list

and then store the p node's reference into the temp node's previous link part.

insertion in doubly linked list

and then we store the node's reference that comes after the node p into the temp node's next link part.

insertion in doubly linked list

and then we store the temp node's reference into the node's previous link part that comes after the node p.

insertion in doubly linked list

and then we store the temp node's reference into the p node's next link part.

insertion in doubly linked list

after completing these steps we now inserted a new node before a node called p in the doubly linked list.


Insert a node before a node in the doubly linked list

like if we want to insert a node before a node called p.

insertion in doubly linked list

first, we allocate a new node called temp.

insertion in doubly linked list

and then we store the node's reference that comes before the node p into the temp node's previous link.

insertion in doubly linked list

and then we store the reference of p node into the temp node's next link part.

insertion in doubly linked list

after that, we store the temp node's reference into the next link part of the node that comes before the node p.

insertion in doubly linked list

after that, we store the temp node's reference into the previous link part of the node p.

insertion in doubly linked list

after performing these steps we now inserted a new node before a node called p.

Python program for inserting a node in the doubly linked list.

class Node(object):

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

class CircularLinkedList(object):

    def __init__(self):
        self.last = None
    def display_list(self):

        if self.last == None:
            print("List is empty\n")
            return
        p = self.last.link

        while True:
            print(p.info, " ", end='')
            p = p.link
            if p == self.last.link:
                break        print()

    def insert_in_beginning(self, data):
        temp = Node(data)
        temp.link = self.last.link
        self.last.link = temp

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

    def insert_at_end(self,data):
        temp = Node(data)
        temp.link = self.last.link
        self.last.link = temp
        self.last = temp

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

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

    def insert_after(self, data, x):
        p = self.last.link

        while True:
            if p.info == x:
                break            p = p.link
            if p == self.last.link:
                break
        if p == self.last.link and p.info != x:
            print(x, " not present in the list")
        else:
            temp = Node(data)
            temp.link = p.link
            p.link = temp
            if p == self.last:
                self.last = temp

    def delete_first_node(self):
        if self.last is None:
            return        if self.last.link == self.last:
            self.last = None            return        self.last.link = self.last.link.link

    def delete_last_node(self):
        if self.last is None:
            return        if self.last.link == self.last:
            self.last = None            return
        p = self.last.link
        while p.link != self.last:
            p = p.link
        p.link = self.last.link
        self.last = p

    def delete_node(self,x):

        if self.last is None:
            return        if self.last.link == self.last and self.last.info == x:
            self.last = None            return        if self.last.link.info == x:
            self.last.link == self.last.link.link
            return
        p = self.last.link
        while p.link != self.last.link:
            if p.link.info == x:
                break            p = p.link

        if p.link == self.last.link:
            print(x, " not found in the list")
        else:
            p.link = p.link.link
            if self.last.info == x:
                self.last = p

#################################################

list = CircularLinkedList()


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. Delete first node")
    print("7. Delete last node")
    print("8. Delete any node")
    print("9. Quite")

    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:
        list.delete_first_node()
    elif option == 7:
        list.delete_last_node()
    elif option == 8:
        data = int(input("Enter the element to be deleted : "))
        list.delete_node(data)
    elif option == 9:
        break    else:
        print("Wrong option")
    print()

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