One-pass algorithm: Difference between revisions
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In computing, a '''one-pass algorithm''' or '''single-pass algorithm''' is a [[streaming algorithm]] which reads its input exactly once.<ref name="frankfurt"/> It does so by processing items in order, without unbounded [[Buffer (computer science)|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.<ref name="sjsu"/> A one-pass algorithm generally requires ''O''(''n'') (see [[Big O Notation|'big O' notation]]) time and less than ''O''(''n'') storage (typically ''O''(1)), where ''n'' is the size of the input.<ref name="eds"/> An example of a one-pass algorithm is the Sondik partially observable |
In computing, a '''one-pass algorithm''' or '''single-pass algorithm''' is a [[streaming algorithm]] which reads its input exactly once.<ref name="frankfurt"/> It does so by processing items in order, without unbounded [[Buffer (computer science)|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.<ref name="sjsu"/> A one-pass algorithm generally requires ''O''(''n'') (see [[Big O Notation|'big O' notation]]) time and less than ''O''(''n'') storage (typically ''O''(1)), where ''n'' is the size of the input.<ref name="eds"/> An example of a one-pass algorithm is the Sondik [[partially observable Markov decision process]].<ref name="pomdp"/> |
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==Example problems solvable by one-pass algorithms== |
==Example problems solvable by one-pass algorithms== |
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Revision as of 04:32, 8 October 2022
 | This article needs additional citations for verification. (April 2021) |
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.
{{cite web}}: CS1 maint: url-status (link) - ^ Pollett, Chris (2005-03-14). "One and Two Pass Algorithms" (PDF). Retrieved 2021-07-01.
{{cite web}}: CS1 maint: url-status (link) - ^ Schweikardt, Nicole (2009), LIU, LING; ÖZSU, M. TAMER (eds.), "One-Pass Algorithm", 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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