To insert an element in a doubly linked list, we first need to create a list:
class Nodeq:
def __init__(self, data):
self.data = data
self.next = None
self.prev = None
There are three ways of inserting an element into a doubly linked list:
insert_beginninginsert_endinsert_after
Insert beginning
Insert beginning is a method to include a new_node in front of the head node and represent new_node as the new head node.
def insert_beginning(self,data):
new_node = Nodeq(data)#creating a node with the given data
if(self.head == None):
self.head = new_node;
return
self.head.prev = new_node
new_node.next = self.head
self.head = new_node #making the new_node as the new head node
Insert end
With the help of insert_end, we can insert elements at the end of the doubly linked list.
def insert_end(self, new_data):
new_node = Nodeq(new_data)
if self.head is None:#checking if the DLL exists
new_node.prev = None
self.head = new_node
return
last = self.head
while last.next:#to asigning the last node to the "last"
last = last.next
last.next = new_node
new_node.prev = last#inserting the new node at the end of the DLL
return
Insert after
With the help of insert_after we can insert after a given element.
prev_datais the given element.
def insert_after(self, prev_data, data):
h=self.head
while h:#searching for the given data
if prev_data == h.data:
break
h=h.next
if h is None:
print("The previous data is not present in the DLL")
return
new_node = Nodeq(data)
# the new_node is inserted after the given node
new_node.next= h.next
h.next=new_node
return
To print the elements in doubly linked list we use Count_Display method.
def Count_Display(self):
if self.head==None: # to check if DLL exists
print("We need a DLL to print")
return
temp = self.head
count=0
while temp:
print (temp.data)#printing node data
count+=1
temp = temp.next
return count
Code
The final code for the insertion of elements in the Doubly Linked List is shown below.
class Nodeq:
def __init__(self, data):
self.data = data
self.next = None
self.prev = None
class DoublyLinkedList:
def __init__(self):
self.head = None
def Count_Display(self):
if self.head==None:
print("We need a DLL to print")
return
temp = self.head
count=0
while temp:
print (temp.data)
count+=1
temp = temp.next
return count
def insert_begining(self,data):
new_node = Nodeq(data)
if(self.head == None):
self.head = new_node
return
self.head.prev = new_node
new_node.next = self.head
self.head = new_node
def insert_end(self, new_data):
new_node = Nodeq(new_data)
if self.head is None:
new_node.prev = None
self.head = new_node
return
last = self.head
while last.next:
last = last.next
last.next = new_node
new_node.prev = last
return
def insert_after(self, prev_data, data):
h=self.head
while h:
if prev_data == h.data:
break
h=h.next
if h is None:
print("The previous Node data must be in the DLL")
return
new_node = Nodeq(data)
new_node.next= h.next
h.next=new_node
return
Dllist = DoublyLinkedList()
Dllist.insert_end(2)
Dllist.insert_begining(3)
Dllist.insert_begining(4)
Dllist.insert_end(5)
Dllist.insert_after(2,0)
print("The number of elements in the DLL list are :",Dllist.Count_Display())
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