Python program to insert a new node at the beginning of the Doubly Linked list
#Represent a node of doubly linked list
class Node:
def __init__(self,data):
self.data = data;
self.previous = None;
self.next = None;
class InsertStart:
#Represent the head and tail of the doubly linked list
def __init__(self):
self.head = None;
self.tail = None;
#addAtStart() will add a node to the starting of the list
def addAtStart(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 head of the list
else:
#head's previous node will be newNode
self.head.previous = newNode;
#newNode's next node will be head
newNode.next = self.head;
#newNode's previous will point to None
newNode.previous = None;
#newNode will become new head
self.head = newNode;
#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 start of the list: ");
while(current != None):
#Prints each node by incrementing pointer.
print(current.data),
current = current.next;
print();
dList = InsertStart();
#Adding 1 to the list
dList.addAtStart(1);
dList.display();
#Adding 2 to the list
dList.addAtStart(2);
dList.display();
#Adding 3 to the list
dList.addAtStart(3);
dList.display();
#Adding 4 to the list
dList.addAtStart(4);
dList.display();
#Adding 5 to the list
dList.addAtStart(5);
dList.display();
Output:
Adding a node to the start of the list:
1
Adding a node to the start of the list:
2 1
Adding a node to the start of the list:
3 2 1
Adding a node to the start of the list:
4 3 2 1
Adding a node to the start of the list:
5 4 3 2 1
