IntroSelector (Lucene 8.1.0 API)

java.lang.Object
- org.apache.lucene.util.Selector
- - org.apache.lucene.util.IntroSelector

```
public abstract class IntroSelector
extends Selector
```
Implementation of the quick select algorithm.
It uses the median of the first, middle and last values as a pivot and falls back to a heap sort when the number of recursion levels exceeds 2 lg(n), as a consequence it runs in linear time on average and in n log(n) time in the worst case.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Constructor Summary

Constructors
Constructor Description

IntroSelector()

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`protected int`	`compare(int i, int j)`	Compare entries found in slots `i` and `j`.
`protected abstract int`	`comparePivot(int j)`	Compare the pivot with the slot at `j`, similarly to `compare(i, j)`.
`void`	`select(int from, int to, int k)`	Reorder elements so that the element at position `k` is 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 to `k` and `(k, to)` only contains elements that are greater than or equal to `k`.
`protected abstract void`	`setPivot(int i)`	Save the value at slot `i` so that it can later be used as a pivot, see `comparePivot(int)`.

Methods inherited from class org.apache.lucene.util.Selector
swap

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - IntroSelector
```
public IntroSelector()
```
- Method Detail
  - select
```
public final void select(int from,
                         int to,
                         int k)
```
    Description copied from class: Selector
    
    Reorder elements so that the element at position k is 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 to k and (k, to) only contains elements that are greater than or equal to k.
    
    Specified by:
    
    select in class Selector
  - compare
```
protected int compare(int i,
                      int j)
```
    Compare entries found in slots i and j. The contract for the returned value is the same as Comparator.compare(Object, Object).
  - setPivot
```
protected abstract void setPivot(int i)
```
    Save the value at slot i so that it can later be used as a pivot, see comparePivot(int).
  - comparePivot
```
protected abstract int comparePivot(int j)
```
    Compare the pivot with the slot at j, similarly to compare(i, j).