One-pass algorithm: Difference between revisions
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== References== |
== References== |
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<ref name="eds">{{Citation|last=Schweikardt|first=Nicole|title=One-Pass Algorithm|date=2009|url=https://doi.org/10.1007/978-0-387-39940-9_253|encyclopedia=Encyclopedia of Database Systems|pages=1948–1949|editor-last=LIU|editor-first=LING|place=Boston, MA|publisher=Springer US|language=en|doi=10.1007/978-0-387-39940-9_253|isbn=978-0-387-39940-9|access-date=2021-04-13|editor2-last=ÖZSU|editor2-first=M. TAMER}}</ref> |
<ref name="eds">{{Citation|last=Schweikardt|first=Nicole|title=One-Pass Algorithm|date=2009|url=https://doi.org/10.1007/978-0-387-39940-9_253|encyclopedia=Encyclopedia of Database Systems|pages=1948–1949|editor-last=LIU|editor-first=LING|editor-link=Ling Liu (computer scientist)|place=Boston, MA|publisher=Springer US|language=en|doi=10.1007/978-0-387-39940-9_253|isbn=978-0-387-39940-9|access-date=2021-04-13|editor2-last=ÖZSU|editor2-first=M. TAMER}}</ref> |
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<ref name="frankfurt">{{Cite web|last=Schweikardt|first=Nicole|title=One-Pass Algorithm|url=http://www.tks.informatik.uni-frankfurt.de/schweika/downloads/EncycDBS_OnePassAlgos.pdf|access-date=2021-07-01}}</ref> |
<ref name="frankfurt">{{Cite web|last=Schweikardt|first=Nicole|title=One-Pass Algorithm|url=http://www.tks.informatik.uni-frankfurt.de/schweika/downloads/EncycDBS_OnePassAlgos.pdf|access-date=2021-07-01}}</ref> |
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<ref name="sjsu">{{Cite web|last=Pollett|first=Chris|date=2005-03-14|title=One and Two Pass Algorithms|url=http://www.cs.sjsu.edu/faculty/pollett/157b.12.05s/Lec14032005.pdf|access-date=2021-07-01}}</ref> |
<ref name="sjsu">{{Cite web|last=Pollett|first=Chris|date=2005-03-14|title=One and Two Pass Algorithms|url=http://www.cs.sjsu.edu/faculty/pollett/157b.12.05s/Lec14032005.pdf|access-date=2021-07-01}}</ref> |
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Revision as of 08:22, 7 December 2023
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In computing, a one-pass algorithm or single-pass algorithm is a streaming algorithm which reads its input exactly once.[1] It does so by processing items in order, without unbounded buffering; it reads a block into an input buffer, processes it, and moves the result into an output buffer for each step in the process.[2] A one-pass algorithm generally requires O(n) (see 'big O' notation) time and less than O(n) storage (typically O(1)), where n is the size of the input.[3] An example of a one-pass algorithm is the Sondik partially observable Markov decision process.[4]
Example problems solvable by one-pass algorithms
Given any list as an input:
- Count the number of elements.
Given a list of numbers:
- Find the k largest or smallest elements, k given in advance.
- Find the sum, mean, variance and standard deviation of the elements of the list. See also Algorithms for calculating variance.
Given a list of symbols from an alphabet of k symbols, given in advance.
- Count the number of times each symbol appears in the input.
- Find the most or least frequent elements.
- Sort the list according to some order on the symbols (possible since the number of symbols is limited).
- Find the maximum gap between two appearances of a given symbol.
Example problems not solvable by one-pass algorithms
Given any list as an input:
- Find the nth element from the end (or report that the list has fewer than n elements).
- Find the middle element of the list. However, this is solvable with two passes: Pass 1 counts the elements and pass 2 picks out the middle one.
Given a list of numbers:
- Find the median.
- Find the modes (This is not the same as finding the most frequent symbol from a limited alphabet).
- Sort the list.
- Count the number of items greater than or less than the mean. However, this can be done in constant memory with two passes: Pass 1 finds the average and pass 2 does the counting.
The two-pass algorithms above are still streaming algorithms but not one-pass algorithms.
References
- ^ Schweikardt, Nicole. "One-Pass Algorithm" (PDF). Retrieved 2021-07-01.
- ^ Pollett, Chris (2005-03-14). "One and Two Pass Algorithms" (PDF). Retrieved 2021-07-01.
- ^ Schweikardt, Nicole (2009), "One-Pass Algorithm", in LIU, LING; ÖZSU, M. TAMER (eds.), Encyclopedia of Database Systems, Boston, MA: Springer US, pp. 1948–1949, doi:10.1007/978-0-387-39940-9_253, ISBN 978-0-387-39940-9, retrieved 2021-04-13
- ^ "Sondik's One-Pass Algorithm". www.pomdp.org.
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