How do you detect a loop in a linked list?

You can detect a loop in a linked list by using two pointers, often referred to as the 'tortoise and the hare' method.

The 'tortoise and the hare' method is a popular technique used to detect a loop in a linked list. It involves two pointers moving at different speeds through the linked list. The first pointer, the 'tortoise', moves one node at a time, while the second pointer, the 'hare', moves two nodes at a time. If there is a loop in the linked list, the 'hare' will eventually meet the 'tortoise' again. If there is no loop, the 'hare' will reach the end of the list without meeting the 'tortoise'.

To implement this method, you would start by setting both pointers at the head of the linked list. Then, in a loop, you would move the 'tortoise' pointer to the next node and the 'hare' pointer two nodes ahead. If at any point the 'hare' pointer is null or the next node of the 'hare' is null, it means the linked list does not have a loop. However, if the 'hare' and 'tortoise' pointers meet, it means there is a loop in the linked list.

This method is efficient because it only requires a constant amount of memory, regardless of the size of the linked list. It also runs in linear time, which means the time it takes to run is proportional to the size of the linked list. This makes it a practical solution for detecting loops in large linked lists.

In conclusion, detecting a loop in a linked list can be achieved by using the 'tortoise and the hare' method. This method is efficient and practical, making it a popular choice for this common problem in computer science.