Cuckoo Cycle is a Proof of Work algorithm in which nodes must compute the shortest path through a graph. This forms the basic unit of work in Cuckoo Cycle, in contrast to the hashing puzzles (such as SHA-256) of many other PoW algorithms. Cuckoo Cycles are memory-hard, as finding the requisite path requires memorizing all attempted paths, as opposed to processor-hard approaches. It was first proposed in 2015, and is used in projects such as Grin for its potential ASIC-resistant characteristics.