Q:

Python program to delete a new node from the end of the doubly linked list

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robaa
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2022-11-08
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In this program, we will create a doubly linked list and delete a node from the end of the list. If the list is empty, print the message "List is empty". If the list is not empty, the tail's previous node will become the new tail of the list thus, deleting the last node from the list.

In the above example, node new was the tail of the list. Make tail's previous node that is, node 4 as the tail of the list. Node 4's next will point to null.

ALGORITHM:

  1. 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.
  2. Define another class for creating the doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
  3. deleteFromEnd() will delete a node from the end of the list:
  • It first checks whether the head is null (empty list) then, it will return from the function as there is no node present in the list.
  • If the list is not empty, it will check whether the list has only one node.
  • If the list has only one node, it will set both head and tail to null.
  • If the list has more than one node then, tail's previous node will become the new tail of the list.
  • This new tail will point to null thus, delete the last node of the list.

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.
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robaa
2022-11-08
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PROGRAM:

#Represent a node of doubly linked list    
class Node:    
    def __init__(self,data):    
        self.data = data;    
        self.previous = None;    
        self.next = None;    
            
class DeleteEnd:    
    #Represent the head and tail of the doubly linked list    
    def __init__(self):    
        self.head = None;    
        self.tail = None;    
            
    #addNode() will add a node to the list    
    def addNode(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;    
        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;    
                
    #deleteFromEnd() will delete a node from the end of the list    
    def deleteFromEnd(self):    
        #Checks whether list is empty    
        if(self.head == None):    
            return;    
        else:    
            #Checks whether the list contains only one node    
            if(self.head != self.tail):    
                #Previous node to the tail will become new tail    
                self.tail = self.tail.previous;    
                #Node next to current tail will be made None    
                self.tail.next = None;    
                    
            #If the list contains only one element     
            #Then it will remove the node, and now both head and tail will point to None    
    
            else:    
                self.head = self.tail = 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;    
        while(current != None):    
            #Prints each node by incrementing pointer.    
            print(current.data),    
            current = current.next;    
        print();    
           
dList = DeleteEnd();    
#Add nodes to the list    
dList.addNode(1);    
dList.addNode(2);    
dList.addNode(3);    
dList.addNode(4);    
dList.addNode(5);    
     
#Printing original list    
print("Original List: ");    
dList.display();    
while(dList.head != None):    
    dList.deleteFromEnd();    
    #Printing updated list    
    print("Updated List: ");    
    dList.display();

 

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 3 4 
Updated List: 
1 2 3 
Updated List: 
1 2 
Updated List: 
1 
Updated List: 
List is empty

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