Zijian Diao Mathematics Department, Ohio University Eastern Campus, St Clairsville, OH 43950, USA∗ Abstract It is well-known that when searching one out of four, the original Grover’s search algorithm is exact; that is, it succeeds with certainty. It is natural to ask the inverse question: If we are not searching one out of four, is Grover’s algorithm definitely not exact? In this article we gi...