This is a Python program to create a doubly linked list and implement insertion, deletion and display operations on the list.
The program creates a doubly linked list and presents the user with a menu to perform various operations on the list.
1. Create a class Node with instance variables data and next.
2. Create a class DoublyLinkedList with instance variables first and last.
3. The variable first points to the first element in the doubly linked list while last points to the last element.
4. Define methods get_node, insert_after, insert_before, insert_at_beg, insert_at_end, remove and display.
5. get_node takes an index as argument and traverses the list from the first node that many times to return the node at that index.
6. The methods insert_after and insert_before insert a node after or before some reference node in the list.
7. The methods insert_at_beg and insert_at_end insert a node at the first or last position of the list.
8. The method remove takes a node as argument and removes it from the list.
9. The method display traverses the list from the first node and prints the data of each node.
10. Create an instance of DoublyLinkedList and present the user with a menu to perform operations on the list.
Here is the source code of a Python program to create a doubly linked list and implement insertion, deletion and display operations on the list. The program output is shown below.
class Node: def __init__(self, data): self.data = data self.next = None self.prev = None class DoublyLinkedList: def __init__(self): self.first = None self.last = None def get_node(self, index): current = self.first for i in range(index): if current is None: return None current = current.next return current def insert_after(self, ref_node, new_node): new_node.prev = ref_node if ref_node.next is None: self.last = new_node else: new_node.next = ref_node.next new_node.next.prev = new_node ref_node.next = new_node def insert_before(self, ref_node, new_node): new_node.next = ref_node if ref_node.prev is None: self.first = new_node else: new_node.prev = ref_node.prev new_node.prev.next = new_node ref_node.prev = new_node def insert_at_beg(self, new_node): if self.first is None: self.first = new_node self.last = new_node else: self.insert_before(self.first, new_node) def insert_at_end(self, new_node): if self.last is None: self.last = new_node self.first = new_node else: self.insert_after(self.last, new_node) def remove(self, node): if node.prev is None: self.first = node.next else: node.prev.next = node.next if node.next is None: self.last = node.prev else: node.next.prev = node.prev def display(self): current = self.first while current: print(current.data, end = ' ') current = current.next a_dllist = DoublyLinkedList() print('Menu') print('insert <data> after <index>') print('insert <data> before <index>') print('insert <data> at beg') print('insert <data> at end') print('remove <index>') print('quit') while True: print('The list: ', end = '') a_dllist.display() print() do = input('What would you like to do? ').split() operation = do[0].strip().lower() if operation == 'insert': data = int(do[1]) position = do[3].strip().lower() new_node = Node(data) suboperation = do[2].strip().lower() if suboperation == 'at': if position == 'beg': a_dllist.insert_at_beg(new_node) elif position == 'end': a_dllist.insert_at_end(new_node) else: index = int(position) ref_node = a_dllist.get_node(index) if ref_node is None: print('No such index.') continue if suboperation == 'after': a_dllist.insert_after(ref_node, new_node) elif suboperation == 'before': a_dllist.insert_before(ref_node, new_node) elif operation == 'remove': index = int(do[1]) node = a_dllist.get_node(index) if node is None: print('No such index.') continue a_dllist.remove(node) elif operation == 'quit': break
1. An instance of DoublyLinkedList is created.
2. The user is presented with a menu to perform various operations on the list.
3. The corresponding methods are called to perform each operation.
Case 1: Menu insert <data> after <index> insert <data> before <index> insert <data> at beg insert <data> at end remove <index> quit The list: What would you like to do? insert 5 at beg The list: 5 What would you like to do? insert 3 at beg The list: 3 5 What would you like to do? insert 1 at end The list: 3 5 1 What would you like to do? insert 10 after 1 The list: 3 5 10 1 What would you like to do? insert 0 before 2 The list: 3 5 0 10 1 What would you like to do? remove 4 The list: 3 5 0 10 What would you like to do? remove 1 The list: 3 0 10 What would you like to do? remove 5 No such index. The list: 3 0 10 What would you like to do? quit Case 2: Menu insert <data> after <index> insert <data> before <index> insert <data> at beg insert <data> at end remove <index> quit The list: What would you like to do? insert 3 after 0 No such index. The list: What would you like to do? insert 2 at beg The list: 2 What would you like to do? insert 3 before 0 The list: 3 2 What would you like to do? remove 0 The list: 2 What would you like to do? remove 0 The list: What would you like to do? quit
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