In this tutorial, we are going to learn how to perform deletion operations in the doubly linked list.

after completing this tutorial you are able to learn how to

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as you see we have a doubly-linked list that has four nodes. so after deleting the first node second node become the first node.

so first we store the second node's reference to the start variable.

and then we set the second node's previous link part to Null or None. because the previous link part of the first node in the doubly linked list is always None or Null.

so after performing these steps, the first node is deleted.

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if a linked list has only one node then to delete this node we set the start variable to the None.

so now our list becomes an empty list.

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to delete a node between two nodes first we need to find out reference to the node that we want to delete. as you see to delete the third node first we found a reference p to that node.

and then we store the reference of the node that comes after node p into the next link part of the node that comes before the node p.

and then we store the reference of the node that comes before node p into the previous link part of the node that comes after node p.

now after performing these steps now, the third node has deleted from the doubly linked list.

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to delete the last node of the list first we need to find out the reference of the last node.

and then we set the next link part of the node to Null or None that come before node p.

so after performing these steps now the last node of the list is deleted.

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after completing this tutorial you are able to learn how to

- Delete the first node.
- Delete the only node.
- Delete a node in between the nodes.
- Delete the last node.

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__Deletion of the first node from the doubly linked list.__

as you see we have a doubly-linked list that has four nodes. so after deleting the first node second node become the first node.so first we store the second node's reference to the start variable.

and then we set the second node's previous link part to Null or None. because the previous link part of the first node in the doubly linked list is always None or Null.

so after performing these steps, the first node is deleted.

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__Delete the only node from the doubly linked list.__

if a linked list has only one node then to delete this node we set the start variable to the None.so now our list becomes an empty list.

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__Delete a node in between the nodes.__

to delete a node between two nodes first we need to find out reference to the node that we want to delete. as you see to delete the third node first we found a reference p to that node.and then we store the reference of the node that comes after node p into the next link part of the node that comes before the node p.

and then we store the reference of the node that comes before node p into the previous link part of the node that comes after node p.

now after performing these steps now, the third node has deleted from the doubly linked list.

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__Delete the last node from the doubly linked list.__

to delete the last node of the list first we need to find out the reference of the last node.and then we set the next link part of the node to Null or None that come before node p.

so after performing these steps now the last node of the list is deleted.

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__Python code to delete the node in the Doubly linked list__

class Node(object): def __init__(self, value): self.info = value self.prev = None self.next = None class DoubleLinkedList(object): def __init__(self): self.start = None def display_list(self): if self.start is None: print("LIst is empty") return print("List is : ") p = self.start while p is not None: print(p.info, " ", end='') p = p.next print() def insert_in_beginning(self, data): temp = None(data) temp.next = self.start self.start.prev = temp self.start = temp def insert_in_empty_list(self, data): temp = Node(data) self.start = temp def insert_at_end(self, data): temp = Node(data) p = self.start while p.next is not None: p = p.next p.next = temp temp.prev = p def create_list(self): n = int(input("Enter the number of nodes : ")) if n == 0: return data = int(input("Enter the first element to be inserted : ")) self.insert_in_empty_list(data) for i in range(n - 1): data = int(input("Enter the next element to be inserted : ")) self.insert_at_end(data) def insert_after(self, data, x): temp = Node(data) p = self.start while p is not None: if p.info == x: break p = p.next if p is None: print(x, " not present in the list") else: temp.prev = p temp.next = p.next if p.next is not None: p.next.prev = temp p.next = temp def insert_before(self, data, x): if self.start is None: print("List is empty") return if self.start.info == x: temp = Node(data) temp.next = self.start self.start.prev = temp self.start = temp return p = self.start while p is not None: if p.info == x: break p = p.next if p is None: print(x, " not present in the list") else: temp = Node(data) temp.prev = p.prev temp.next = p p.prev.next = temp p.prev = temp def delete_first_node(self): if self.start is None: return if self.start.next is None: self.start = None return self.start = self.start.next self.start.prev = None def delete_last_node(self): if self.start is None: return if self.start.next is None: self.start = None return p = self.start while p.next != None: p = p.next p.prev.next = None def delete_node(self, x): if self.start is None: return if self.start.next is None: if self.start.info == x: self.start = None else: print(x, " not found") return if self.start.info == x: self.start = self.start.next self.start.prev = None return p = self.start.next while p.next is not None: if p.info == x: break p = p.next if p.next is not None: p.prev.next = p.next p.next.prev = p.prev else: if p.info == x: p.prev.next else: print(x, " not found") def reverse_list(self): if self.start is None: return p1 = self.start p2 = p1.next p1.next = None p1.prev = p2 while p2 is not None: p2.prev = p2.next p2.next = p1 p1 = p2 p2 = p2.prev self.start = p1 #################################################################3 list = DoubleLinkedList() 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. Insert a node before a specified node") print("7. Delete first node") print("8. Delete last node") print("9. Delete any node") print("10. Reverse the list") print("11. 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_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: data = int(input("Enter the element to be inserted : ")) x = int(input("Enter the element before which to inserted : ")) list.insert_before(data, x) elif option == 7: list.delete_first_node() elif option == 8: list.delete_last_node() elif option == 9: data = int(input("Enter the element to be deleted : ")) list.delete_node(data) elif option == 10: list.reverse_list() elif option == 11: break else: print("Wrong option") print()

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