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Python Linked Lists

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A Linked List is a linear data structure where elements (called nodes) are connected using pointers.

Each node contains:

  • Data

  • A pointer to the next node

It follows a sequential order, but unlike arrays, it does not use continuous memory.

🔹 Why Use Linked Lists?

  • Dynamic size

  • Efficient insert/delete from start or middle

  • No need to shift elements (like in arrays)

🔹 Node Structure

A simple node in Python is created using a class:

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

🔹 Create a Linked List

# Define node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# Create linked list
node1 = Node(10)
node2 = Node(20)
node3 = Node(30)

# Connect nodes
node1.next = node2
node2.next = node3

# Traverse list
current = node1
while current:
    print(current.data)
    current = current.next

✅ Output:

10
20
30

🔹 Operations on Linked List

1. Traversal
def traverse(head):
    current = head
    while current:
        print(current.data)
        current = current.next
2. Insert at Beginning
new_node = Node(5)
new_node.next = node1  # node1 was the previous head
head = new_node
3. Insert at End
def insert_end(head, data):
    new = Node(data)
    current = head
    while current.next:
        current = current.next
    current.next = new
4. Delete a Node
def delete_node(head, key):
    if head.data == key:
        return head.next
    prev = None
    current = head
    while current and current.data != key:
        prev = current
        current = current.next
    if current:
        prev.next = current.next
    return head

Practice Questions

Q1. Write a Python program to create a linked list with 4 nodes having values: 10, 20, 30, and 40.

Q2. Write a Python program to define a function that displays all values in the linked list.

Q3. Write a Python program to insert a new node at the beginning of the linked list.

Q4. Write a Python program to insert a new node at the end of the linked list.

Q5. Write a Python program to delete a node with value 20 from the linked list.

Q6. Write a Python program to count the total number of nodes in the linked list.

Q7. Write a Python program to check if a specific value exists in the linked list.

Q8. Write a Python program to reverse the linked list.

Q9. Write a Python program to create a function that searches a node by value and returns its position.

Q10. Write a Python program to print the value of the last node in the linked list.

Python Linked Lists Quiz

Q1: What is a Linked List?

A. A fixed array
B. A sequential data structure using pointers
C. A binary tree
D. A sorted list

Q2: What does each node contain?

A. Only data
B. Data and previous pointer
C. Data and next pointer
D. Only pointer

Q3: What is the last node of a linked list?

A. The head
B. Node with no data
C. Node whose next is None
D. Node with 0

Q4: How do you access the middle node of a list?

A. head.next
B. Traverse till middle
C. index[]
D. Reverse list

Q5: Which operation is efficient in a linked list?

A. Access by index
B. Random insert
C. Insert/delete at beginning
D. All are same

Q6: What is the time complexity of traversal in linked list?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Q7: Can a linked list store different data types?

A. Yes
B. No
C. Only integers and strings
D. Only if implemented using arrays

Q8: What is the starting node called?

A. Root
B. Head
C. Base
D. Top

Q9: Can a linked list store different data types?

A. Yes
B. No
C. Only integers and strings
D. Only if implemented using arrays

Q10: Which module is needed for linked lists in Python?

A. array
B. list
C. None (custom class)
D. collections
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