public class Median
extends java.lang.Object
Modifier | Constructor and Description |
---|---|
private |
Median()
This class is supposed to have static methods only.
|
Modifier and Type | Method and Description |
---|---|
static int |
find(int[] a,
int from,
int to)
Find the median value of the specified interval of the argument array.
|
static void |
swap(int[] a,
int i1,
int i2)
Exchange two elements in the argument array.
|
private Median()
public static void swap(int[] a, int i1, int i2)
a
- the array in which two elements are swappedi1
- index of the first elementi2
- index of the second elementjava.lang.ArrayIndexOutOfBoundsException
- if either i1 or i2 are
not valid index values into a (from 0 to a.length - 1)public static int find(int[] a, int from, int to)
from
and goes to
to
; the values at these positions are included.
Note that the array will be modified while searching, so you might want
to backup your data.
This implementation is a port of the C function from
quickselect.c
, provided at http://ndevilla.free.fr/median/.
The page is a good resource for various median value algorithms, including
implementations and benchmarks.
The original code on which this class is based was written in C++ by Martin Leese. It was ported to C and optimized by Nicolas Devillard (author of the above mentioned page). The algorithm is from Numerical recipes in C, Second Edition, Cambridge University Press, 1992, Section 8.5, ISBN 0-521-43108-5.
a
- the arrayfrom
- the index of the start of the interval in which the median value will be searchedto
- the index of the end of the interval in which the median value will be searched