In quantum computing, the Brasard-Hoyer-Tappar algorithm or BHT algorithm is a quantum algorithm that solves the collision problem. In this problem, one is given n and an r-to-1 function and needs to find two inputs that f maps to the same output. The BHT algorithm only makes queries to f, which matches the lower bound of in the black box model. The algorithm was discovered by Gilles Brassard, Peter Hoyer, and Alain Tapp in 1997. It uses Grover's algorithm, which was discovered in the previous year.