a pointer algorithm that uses only two pointers, which move through the sequence at different speeds. - Cycle detection

There are 3 steps:

• find if cycle exists
• find position of first repetition
• find cycle length

see also

• rosettacode.org

• Brent’s algorithm use a faster model with progressive speed.

• If Programming Was An Anime
• Possibly all the ways to get loop-finding in graphs wrong / HN