How to determine if a given linked list contains a loop, and how would you remove the loop?

Question

Aryan Kumar · Answer

There are two common ways to determine if a given linked list contains a loop:

Floyd's cycle detection algorithm: This algorithm uses two pointers, one fast and one slow. The fast pointer moves two nodes at a time, while the slow pointer moves one node at a time. If the two pointers ever meet, then the linked list contains a loop.

Using a hash table: This algorithm stores the addresses of all the nodes in a hash table. If the same node is encountered twice, then the linked list contains a loop.

To remove the loop from a linked list, you can use the following steps:

Find the starting node of the loop: You can use either of the two methods mentioned above to find the starting node of the loop.

Break the loop: Once you have found the starting node of the loop, you can break it by setting the next pointer of the node to null.

Here is an example of how to determine if a linked list contains a loop and remove it in Python:

Python

def is_loop_exists(head):
    slow = head
    fast = head

    while slow and fast and fast.next:
        slow = slow.next
        fast = fast.next.next

        if slow == fast:
            return True

    return False


def remove_loop(head):
    slow = head
    fast = head

    while slow and fast and fast.next:
        slow = slow.next
        fast = fast.next.next

        if slow == fast:
            break

    while slow.next != fast.next:
        slow = slow.next
        fast = fast.next

    slow.next = None

Here is an explanation of the code:

The is_loop_exists() function uses Floyd's cycle detection algorithm to determine if the linked list contains a loop.
The remove_loop() function uses the following steps to remove the loop from the linked list:
1. Find the starting node of the loop using the is_loop_exists() function.
2. Set the next pointer of the starting node to null.

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How to determine if a given linked list contains a loop, and how would you remove the loop?

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