Ask HN: What are your favorite algorithms?

Token Bucket. Very lightweight way to implement rate limiting.

PHP implementation: https://github.com/bandwidth-throttle/token-bucket

ROAM: Real-time Optimally Adapting Meshes https://graphics.llnl.gov/ROAM/roam.pdf

Whitted's recursive ray tracing algorithm https://en.wikipedia.org/wiki/Ray_tracing_(graphics)#Recursi...

PageRank

The Fastest and Shortest Algorithm for All Well-Defined Problems: https://arxiv.org/abs/cs/0206022

Abstract: An algorithm M is described that solves any well-defined problem p as quickly as the fastest algorithm computing a solution to p, save for a factor of 5 and low-order additive terms. M optimally distributes resources between the execution of provably correct p-solving programs and an enumeration of all proofs, including relevant proofs of program correctness and of time bounds on program runtimes. M avoids Blum's speed-up theorem by ignoring programs without correctness proof. M has broader applicability and can be faster than Levin's universal search, the fastest method for inverting functions save for a large multiplicative constant. An extension of Kolmogorov complexity and two novel natural measures of function complexity are used to show that the most efficient program computing some function f is also among the shortest programs provably computing f.

The catch is that the constants in the big-O are enormous.

Also, fft gets an obligatory mention

Contrastive divergence for RBMs. Incredibly simple, but absolutely beautiful how it modifies the energy surface. Also, just in general a cool use of Gibbs sampling.