Quantum counting solves a generalization of the the search problem. It solves the problem of counting the number of marked entries in an unordered list. Specifically, it counts the number of marked entries in an <math>N</math>-element list, with error <math>\epsilon</math> making only <math>\Theta\left(\frac{1}{\epsilon} \sqrt{\frac{N}{k}}\right)</math> queries, where <math>k</math> is the number of marked elements in the list.<ref>{{Cite journal
