Python Linked List: Insert an item in front of a given doubly linked list

Last update on December 21 2024 07:26:30 (UTC/GMT +8 hours)

Write a Python program to insert an item in front of a given doubly linked list.

Sample Solution:

Python Code:

class Node(object):
    # Singly linked node
    def __init__(self, data=None, next=None, prev=None):
        self.data = data
        self.next = next
        self.prev = prev

class doubly_linked_list(object):
    def __init__(self):
        self.head = None
        self.tail = None
        self.count = 0

    def append_item(self, data):
        # Append an item 
        new_item = Node(data, None, None)
        if self.head is None:
            self.head = new_item
            self.tail = self.head
        else:
            new_item.prev = self.tail
            self.tail.next = new_item
            self.tail = new_item
        self.count += 1
    
    def iter(self):
        # Iterate the list
        current = self.head
        while current:
            item_val = current.data
            current = current.next
            yield item_val

    def print_foward(self):
        for node in self.iter():
            print(node)   
        
    def insert_start(self, data):        
        if self.head is not None:
            new_node = Node(data, None, None)
            new_node.next = self.head
            self.head.prev = new_node
            self.head = new_node
            self.count += 1

items = doubly_linked_list()
items.append_item('PHP')
items.append_item('Python')
items.append_item('C#')
items.append_item('C++')
items.append_item('Java')
items.append_item('SQL')

print("Original list:")
items.print_foward()
print("\nAppend item in front of the list:")
items.insert_start("Perl")
items.print_foward()

Sample Output:

Original list:
PHP
Python
C#
C++
Java
SQL

Append item in front of the list:
Perl
PHP
Python
C#
C++
Java
SQL

Flowchart:

Python Code Editor:

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