Python program to insert a new node at the end of the Doubly Linked List.

In this program, we will create a doubly linked list and insert every new node at the end of the list. If the list is empty, then head and tail will point to the newly added node. If the list is not empty then, insert the new node at the end of the list such that tail's next will point to new node. Make new node as the new tail of the list, and its next will point to null.

In the above example, node 4 was the tail of the list. Now, the new node will be inserted at the end of the list such that node 4's next will point to the new node. Make new node as the tail of the list, and its next will point to null.

ALGORITHM:

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
addAtEnd() will add node to the list:

It first checks whether the head is null, then it will insert the node as the head.
Both head and tail will point to a newly added node.
Head's previous pointer will point to null and tail's next pointer will point to null.
If the head is not null, the new node will be inserted at the end of the list such that new node's previous pointer will point to tail.
The new node will become the new tail. Tail's next pointer will point to null.

a. display() will show all the nodes present in the list.

Define a new node 'current' that will point to the head.
Print current.data till current points to null.
Current will point to the next node in the list in each iteration.

PROGRAM:

#Represent a node of doubly linked list  
class Node:  
    def __init__(self,data):  
        self.data = data;  
        self.previous = None;  
        self.next = None;  
          
class InsertEnd:  
    #Represent the head and tail of the doubly linked list  
    def __init__(self):  
        self.head = None;  
        self.tail = None;  
          
    #addAtEnd() will add a node to the end of the list  
    def addAtEnd(self, data):  
        #Create a new node  
        newNode = Node(data);  
          
        #If list is empty  
        if(self.head == None):  
            #Both head and tail will point to newNode  
            self.head = self.tail = newNode;  
            #head's previous will point to None  
            self.head.previous = None;  
            #tail's next will point to None, as it is the last node of the list  
            self.tail.next = None;  
        #Add newNode as new tail of the list  
        else:  
            #newNode will be added after tail such that tail's next will point to newNode  
            self.tail.next = newNode;  
            #newNode's previous will point to tail  
            newNode.previous = self.tail;  
            #newNode will become new tail  
            self.tail = newNode;  
            #As it is last node, tail's next will point to None  
            self.tail.next = None;  
              
    #display() will print out the nodes of the list  
    def display(self):  
        #Node current will point to head  
        current = self.head;  
        if(self.head == None):  
            print("List is empty");  
            return;  
        print("Adding a node to the end of the list: ");  
        while(current != None):  
            #Prints each node by incrementing pointer.  
            print(current.data),  
            current = current.next;  
              
        print();  
          
dList = InsertEnd();  
   
#Adding 1 to the list  
dList.addAtEnd(1);  
dList.display();  
#Adding 2 to the list  
dList.addAtEnd(2);  
dList.display();  
#Adding 3 to the list  
dList.addAtEnd(3);  
dList.display();  
#Adding 4 to the list  
dList.addAtEnd(4);  
dList.display();  
#Adding 5 to the list  
dList.addAtEnd(5);  
dList.display();  

Output:

Adding a node to the end of the list: 
1 
Adding a node to the end of the list: 
1 2 
Adding a node to the end of the list: 
1 2 3 
Adding a node to the end of the list: 
1 2 3 4 
Adding a node to the end of the list: 
1 2 3 4 5

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