  We propose a quantum algorithm for closest pattern matching which allows us
to search for as many distinct patterns as we wish in a given string
(database), requiring a query function per symbol of the pattern alphabet. This
represents a significant practical advantage when compared to Grover's search
algorithm as well as to other quantum pattern matching methods, which rely on
building specific queries for particular patterns. Our method makes arbitrary
searches on long static databases much more realistic and implementable. Our
algorithm, inspired by Grover's, returns the position of the closest substring
to a given pattern of size $M$ with non-negligible probability in $O(\sqrt{N})$
queries, where $N$ is the size of the string. Furthermore, we give the full
recipe to implement our algorithm (together with its total circuit complexity),
thus offering an oracle-based quantum algorithm ready to be implemented.
