Floyd Cycle
In plain terms
A two-pointer method to detect cycles using fast and slow pointers.
Going deeper
Floyd's tortoise-and-hare algorithm advances one pointer twice as fast as another; if they meet, there's a cycle. It uses constant memory.
Under the hood
O(n) time, O(1) space; also finds the cycle's start and length.
Examples
Linked-list cycle detection, finding loops, duplicate-number problems.
Think of it like...
Like two runners on a loop track: the faster one eventually laps and meets the slower if the track is circular.