# 1. Introduction

Linked lists are among the fundamental data structures used in computer science. However, due to some programming errors or other factors, linked lists may sometimes contain loops, which can lead to various problems. In this post, we will implement and understand an algorithm to detect and remove a loop from a linked list.

# 2. Program Overview

1. Define the Node and LinkedList classes.

2. Implement the method to add nodes to the linked list.

3. Implement Floyd’s cycle-finding algorithm (also known as the "Tortoise and the Hare" algorithm) to detect the loop.

4. Once the loop is detected, remove the loop.

5. Demonstrate the program using a sample linked list.

# 3. Code Program

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

def __init__(self):

def append(self, data):
"""Add a node to the end of the linked list."""
new_node = Node(data)
return
while last_node.next:
last_node = last_node.next
last_node.next = new_node

def detect_and_remove_loop(self):
"""Detect and remove loop from the linked list."""
return

# Initialize slow and fast pointers

# Move slow by one and fast by two steps
while fast and fast.next:
slow = slow.next
fast = fast.next.next

# If they meet, then loop is detected
if slow == fast:
self.remove_loop(slow)
return True  # Loop found
return False  # No loop

def remove_loop(self, loop_node):
"""Remove loop in the linked list using the loop node."""
ptr2 = loop_node

# Find the starting point of the loop
while True:
ptr2 = loop_node
while ptr2.next != ptr1 and ptr2.next != loop_node:
ptr2 = ptr2.next
if ptr2.next == ptr1:
break
ptr1 = ptr1.next

# Remove the loop by setting the next of loop node to None
ptr2.next = None

# Sample linked list with loop
ll.append(1)
ll.append(2)
ll.append(3)
ll.append(4)
ll.append(5)
# Introducing loop: last node points back to the third node
loop_found = ll.detect_and_remove_loop()
print("Loop Detected:", loop_found)
if loop_found:
print("Loop Removed!")
``````

### Output:

```Loop Detected: True
Loop Removed!
```

# 4. Step By Step Explanation

1. We begin by defining the basic structures of Node and LinkedList.

2. We have an append method to add nodes to the end of our linked list.

3. The main functionality lies in detect_and_remove_loop. We use Floyd's cycle-finding algorithm to detect the loop. It uses two pointers moving through the sequence at different speeds.

4. Once a loop is detected (i.e., the slow pointer meets the fast pointer), we use the remove_loop method to identify the loop's starting point and remove the loop by setting the appropriate node's next pointer to None.

5. Our sample linked list demonstrates a loop, and we successfully detect and remove it.