How can 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 "slow" and "fast" pointers. The slow pointer moves one node at a time, while the fast pointer moves two nodes at a time. If there is a loop in the linked list, these pointers will eventually meet at the same node. This approach is known as Floyd's Cycle Detection Algorithm and is efficient in detecting loops without requiring extra space. Using a hash table to store visited nodes can also detect loops but requires O(n) extra space, whereas Floyd's Algorithm only requires constant space.