**as we know in the node of the doubly linked list we have two link parts and one info part. and every node holds the reference of the previous and next node.**

__Insertion in a doubly-linked list:__so to insert the new node at any position like at the first position, the last position, in between the nodes and before and after the node we need to maintain both references.

so after completing this tutorial, you will be able to learn about

- Insert node at the beginning of the linked list
- Insert node in an empty list.
- Insert node at the end of the list.
- Insert node after a node.
- Insert node before a node.

###
__Inserting a node at the beginning of the doubly linked list.__

to insert a node at the beginning of the list first we allocate a new node called temp. as you see in the image given below.

and then we store the new node temp's reference in the first node of the list. as you see in the image given below.

###
__Insert a node in an empty doubly-linked list.__

as we know we don't have any node in an empty list.

so to insert a node in an empty list first we allocate a new node called temp and store the reference of the new node in the start variable.

###
__Insert a node at the end of the doubly linked list.__

to insert a new node at the end of the list first we need a reference of the last node of the doubly linked list. so we find a reference for the last node called p.

###
__Insert a node after a node in the doubly linked list.__

like if we want to insert a node after a node called p.

and then we store the node's reference that comes after the node p into the temp node's next link part.

and then we store the temp node's reference into the node's previous link part that comes after the node p.

after completing these steps we now inserted a new node before a node called p in the doubly linked list.

###
__Insert a node before a node in the doubly linked list__

like if we want to insert a node before a node called p.

and then we store the node's reference that comes before the node p into the temp node's previous link.

after that, we store the temp node's reference into the next link part of the node that comes before the node p.

####
__Python program for inserting a node in the doubly linked list.__

class Node(object): def __init__(self, value): self.info = value self.link = None class CircularLinkedList(object): def __init__(self): self.last = None def display_list(self): if self.last == None: print("List is empty\n") return p = self.last.link while True: print(p.info, " ", end='') p = p.link if p == self.last.link: break print() def insert_in_beginning(self, data): temp = Node(data) temp.link = self.last.link self.last.link = temp def insert_in_empty_list(self, data): temp = Node(data) self.last = temp self.last.link = self.last def insert_at_end(self,data): temp = Node(data) temp.link = self.last.link self.last.link = temp self.last = temp def create_list(self): n = int(input("Enter the number of nodes : ")) if n == 0: return data = int(input("Enter the element to be inserted : ")) self.insert_in_empty_list(data) for i in range(n-1): data = int(input("Enter the element to be inserted : ")) self.insert_at_end(data) def insert_after(self, data, x): p = self.last.link while True: if p.info == x: break p = p.link if p == self.last.link: break if p == self.last.link and p.info != x: print(x, " not present in the list") else: temp = Node(data) temp.link = p.link p.link = temp if p == self.last: self.last = temp def delete_first_node(self): if self.last is None: return if self.last.link == self.last: self.last = None return self.last.link = self.last.link.link def delete_last_node(self): if self.last is None: return if self.last.link == self.last: self.last = None return p = self.last.link while p.link != self.last: p = p.link p.link = self.last.link self.last = p def delete_node(self,x): if self.last is None: return if self.last.link == self.last and self.last.info == x: self.last = None return if self.last.link.info == x: self.last.link == self.last.link.link return p = self.last.link while p.link != self.last.link: if p.link.info == x: break p = p.link if p.link == self.last.link: print(x, " not found in the list") else: p.link = p.link.link if self.last.info == x: self.last = p ################################################# list = CircularLinkedList() list.create_list() while True: print("1. Display list") print("2. Insert in empty list") print("3. Insert a node in the beginning of the list") print("4. Insert a node at the end of the list") print("5. Insert a node after a specified node") print("6. Delete first node") print("7. Delete last node") print("8. Delete any node") print("9. Quite") 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_in_empty_list(data) elif option == 3: data = int(input("Enter the element to be inserted : ")) list.insert_in_beginning(data) elif option == 4: data = int(input("Enter the element to be inserted : ")) list.insert_at_end(data) elif option == 5: data = int(input("Enter the element to be inserted : ")) x = int(input("Enter the element after which to insert : ")) list.insert_after(data,x) elif option == 6: list.delete_first_node() elif option == 7: list.delete_last_node() elif option == 8: data = int(input("Enter the element to be deleted : ")) list.delete_node(data) elif option == 9: break else: print("Wrong option") print()

## 0 Comments