An algorithm for finding nearest neighbours in constant average time with a linear space complexity

Given a set of n points or 'prototypes' and another point or 'test sample'. The authors present an algorithm that finds a prototype that is a nearest neighbour of the test sample, by computing only a constant number of distances on the average. This is achieved through a preprocessing procedure that computes only a number of distances and uses an amount of memory that grows lineally with n. The algorithm is an improvement of the previously introduced AESA algorithm and, as such, does not assume the data to be structured into a vector space, making only use of the metric properties of the given distance.<>