Create and Initialize Doubly Linked List in DSA Python - Build from Scratch

Create and Initialize Doubly Linked List

📖 Scenario: You are building a simple contact list app. Each contact will be stored in a doubly linked list node, allowing easy navigation forward and backward through contacts.

🎯 Goal: Create a doubly linked list with three contacts: Alice, Bob, and Charlie. Initialize the list so each node points correctly to the next and previous contacts.

📋 What You'll Learn

Define a Node class with data, prev, and next attributes

Create three nodes with data 'Alice', 'Bob', and 'Charlie'

Link the nodes so that Alice is first, Bob is second, and Charlie is third

Ensure prev and next pointers are correctly set for each node

💡 Why This Matters

🌍 Real World

Doubly linked lists are used in music players to move forward and backward through songs, or in browsers to navigate back and forth through pages.

💼 Career

Understanding doubly linked lists helps in jobs involving data structure design, memory management, and building efficient navigation systems.

1

Define the Node class

Define a class called Node with an __init__ method that takes data as a parameter and initializes self.data, self.prev, and self.next to None.

DSA Python

# Define the Node class with __init__ method
# Your code here

Hint

Think of each node as a box holding data and two pointers: one to the previous box and one to the next box.

2

Create three nodes for contacts

Create three variables called node1, node2, and node3 and assign them new Node objects with data 'Alice', 'Bob', and 'Charlie' respectively.

DSA Python

class Node:
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None

# Create three nodes with data 'Alice', 'Bob', and 'Charlie'
# Your code here

Hint

Use the Node class to create each contact node with the exact names and data.

3

Link the nodes to form the doubly linked list

Set node1.next to node2, node2.prev to node1, node2.next to node3, and node3.prev to node2 to link the nodes in order.

DSA Python

class Node:
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None

node1 = Node('Alice')
node2 = Node('Bob')
node3 = Node('Charlie')

# Link the nodes to form the doubly linked list
# Your code here

Hint

Remember, each node's next points forward and prev points backward.

4

Print the doubly linked list forward and backward

Use a current variable starting at node1 to print the list forward by following next pointers. Then use current starting at node3 to print the list backward by following prev pointers. Print the data values separated by -> and end with null.

DSA Python

class Node:
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None

node1 = Node('Alice')
node2 = Node('Bob')
node3 = Node('Charlie')

node1.next = node2
node2.prev = node1
node2.next = node3
node3.prev = node2

# Print the list forward and backward
# Your code here

Hint

Use a loop to move through the list using next for forward and prev for backward printing.