Editing Quantum algorithm (section)

===Quantum counting===
[[Quantum counting]] solves a generalization of the search problem. It solves the problem of counting the number of marked entries in an unordered list, instead of just detecting whether one exists. Specifically, it counts the number of marked entries in an <math>N</math>-element list with an error of at most <math>\varepsilon</math> by making only <math>\Theta\left(\varepsilon^{-1} \sqrt{N/k}\right)</math> queries, where <math>k</math> is the number of marked elements in the list.<ref>
{{Cite book
 |last1 = Brassard |first1 = G.
 |last2=Hoyer |first2=P.
 |last3=Tapp |first3=A.
 |chapter = Quantum counting
 |date = 1998
 |title = Automata, Languages and Programming
 |arxiv = quant-ph/9805082
 |doi=10.1007/BFb0055105
 |volume = 1443
 |pages=820–831
|series = Lecture Notes in Computer Science
 |isbn = 978-3-540-64781-2
 |s2cid = 14147978
 }}</ref><ref>
{{Cite book
 |last1=Brassard |first1=G.
 |last2=Hoyer |first2=P.
 |last3=Mosca |first3=M.
 |last4=Tapp |first4=A.
 |year=2002
 |chapter=Quantum Amplitude Amplification and Estimation
 |title=Quantum Computation and Quantum Information
 |editor=Samuel J. Lomonaco, Jr.
 |series=AMS Contemporary Mathematics
 |volume=305
 |pages=53–74
 |doi=10.1090/conm/305/05215
 |arxiv=quant-ph/0005055
|bibcode=2000quant.ph..5055B|isbn=9780821821404
 |s2cid=54753
 }}</ref> More precisely, the algorithm outputs an estimate <math>k'</math> for <math>k</math>, the number of marked entries, with accuracy <math>|k-k'| \leq \varepsilon k</math>.