Package org.apache.lucene.util
Class IntroSelector
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- org.apache.lucene.util.Selector
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- org.apache.lucene.util.IntroSelector
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public abstract class IntroSelector extends Selector
Adaptive selection algorithm based on the introspective quick select algorithm. The quick select algorithm uses an interpolation variant of Tukey's ninther median-of-medians for pivot, and Bentley-McIlroy 3-way partitioning. For the introspective protection, it shuffles the sub-range if the max recursive depth is exceeded.This selection algorithm is fast on most data shapes, especially on nearly sorted data, or when k is close to the boundaries. It runs in linear time on average.
- NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.
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Constructor Summary
Constructors Constructor Description IntroSelector()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description protected intcompare(int i, int j)Compare entries found in slotsiandj.protected abstract intcomparePivot(int j)Compare the pivot with the slot atj, similarly tocompare(i, j).voidselect(int from, int to, int k)Reorder elements so that the element at positionkis the same as if all elements were sorted and all other elements are partitioned around it:[from, k)only contains elements that are less than or equal tokand(k, to)only contains elements that are greater than or equal tok.protected abstract voidsetPivot(int i)Save the value at slotiso that it can later be used as a pivot, seecomparePivot(int).
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Method Detail
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select
public final void select(int from, int to, int k)Description copied from class:SelectorReorder elements so that the element at positionkis the same as if all elements were sorted and all other elements are partitioned around it:[from, k)only contains elements that are less than or equal tokand(k, to)only contains elements that are greater than or equal tok.
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setPivot
protected abstract void setPivot(int i)
Save the value at slotiso that it can later be used as a pivot, seecomparePivot(int).
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comparePivot
protected abstract int comparePivot(int j)
Compare the pivot with the slot atj, similarly tocompare(i, j).
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compare
protected int compare(int i, int j)Compare entries found in slotsiandj. The contract for the returned value is the same asComparator.compare(Object, Object).
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