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In computing, a one-pass algorithm is one which reads its input exactly once, in order, without unbounded buffering. 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. Basically one-pass algorithm operates as follows: (1) the object descriptions are processed serially; (2) the first object becomes the cluster representative of the first cluster; (3) each subsequent object is matched against all cluster representatives existing at its processing time; (4) a given object is assigned to one cluster (or more if overlap is allowed) according to some condition on the matching function; (5) when an object is assigned to a cluster the representative for that cluster is recomputed; (6) if an object fails a certain test it becomes the cluster representative of a new cluster ==Example problems solvable by one-pass algorithms== Given any list as an input: * Count the number of elements. * Find the ''n''th element (or report that the list has fewer than ''n'' elements). * Find the ''n''th element from the end (or report that the list has fewer than ''n'' 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. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「One-pass algorithm」の詳細全文を読む スポンサード リンク
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