In Data Structure The header linked list is a list that has a header node at the beginning of the linked list. and the head always refers to the header node of the list.
What is Header Node
the info part of the header node is always None. Therefore we can use this part to store some useful information about the linked list. like storing the number of nodes in a list and some of the values of the linked list etc.
and the linked part of the header node is always referred to as the first node of the linked list.
Advantages of Header Linked List
If the list is empty then always the header node is available in the linked list. so we don’t need to check whether the linked list is empty or not.
we can easily perform operations like insertion and deletion because we don’t need to check if the list is empty or not.
Header Linked List program in Python.
class Node(object):
def __init__(self,value):
self.info = value
self.link = None
class HeaderLinkedList(object):
def __init__(self):
self.head = Node(0)
def display_list(self):
if self.head.link == None:
print("List is empty")
return
p =self.head.link
print("List is : ")
while p is not None:
print(p.info, " ",end='')
p = p.link
print()
def create_list(self):
n = int(input("Enter the number of nodes : "))
for i in range(n):
data = int(input("Enter the element to be inserted : "))
self.insert_at_end(data)
def insert_at_end(self,data):
temp = Node(data)
p = self.head
while p.link is not None:
p = p.link
p.link = temp
def insert_before(self,data,x):
p = self.head
while p.link is not None:
if p.link.info == x:
break p = p.link
if p.link is None:
print(x, " not present in the list")
else:
temp = Node(data)
temp.link = p.link
p.link = temp
def insert_at_position(self,data,x):
p = self.head
i = 1 while i <= k-1 and p is not None:
p = p.link
i += 1
if p is None:
print("You can insert only upto ", (i-1), " th position")
else:
temp = Node(data)
temp.link = p.link
p.link = temp
def delete_node(self,data):
p = self.head
while p.link is not None:
if p.link.info == data:
break p = p.link
if p.link == None:
print(data, " not found")
else:
p.link = p.link.link
def reverse_list(self):
prev = None p = self.head.link
while p is not None:
next = p.link
p.link = prev
prev = p
p = next
self.head.link = prev
list = HeaderLinkedList()
list.create_list()
while True:
print("1. Display list")
print("2. Insert a node at the end of the list")
print("3. Insert a node before a specified node")
print("4. Insert a node at a given position")
print("5. Delete a node")
print("6. Reverse the list")
print("9. Quit")
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_at_end(data)
elif option == 3:
data = int(input("Enter the element to be inserted : "))
x = int(input("Enter the element before which to insert : "))
list.insert_before(data,x)
elif option == 4:
data = int(input("Enter the element to be inserted : "))
k = int(input("Enter the position at which to insert : "))
list.insert_at_position(data,x)
elif option == 5:
data = int(input("Enter the element to be deleted : "))
list.delete_node(data)
elif option == 7:
break else:
print("Wrong option")
print()
