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https://issues.apache.org/jira/browse/ARROW-7400?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated ARROW-7400:
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Labels: pull-request-available (was: )
> [Java] Avoids the worst case for quick sort
> -------------------------------------------
>
> Key: ARROW-7400
> URL: https://issues.apache.org/jira/browse/ARROW-7400
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Java
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Labels: pull-request-available
>
> This issue is in response of a discussion in:
> https://github.com/apache/arrow/pull/5540#discussion_r329487232.
> The quick sort algorithm can degenerate to an O(n^2) algorithm, if the pivot
> is selected poorly. This is an important problem, as the worst case can
> happen, if the input vector is alrady sorted, which is frequently encountered
> in practice.
> After some investigation, we solve the problem with a simple but effective
> approach: take 3 samples and choose the median (with at most 3 comparisons)
> as the pivot. This sorts the vector which is already sorted in O(nlogn) time.
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