Package org.aksw.commons.util.math

Class Lehmer

java.lang.Object

org.aksw.commons.util.math.Lehmer

public class Lehmer
extends Object

Class for computing the lehmer code and value for a given set of items w.r.t. a comparator. The lehmer code is a basis for numbering permutations. The (decimal) value of a lehmer code for n items ranges from 0 to n!. The value is 0 for a sorted sequence of items and n! for a reverse-sorted one.

Constructor Summary

Constructors

Constructor	Description
Lehmer()

Method Summary

Modifier and Type	Method	Description
static <T> int[]	lehmerCode(Collection<T> items, Comparator<T> comparator)	For a given collection of unique items with a defined total ordering (via comparator) compute the natural number that correspends to n-th permutation w.r.t.
static <T> BigInteger	lehmerValue(Collection<T> items, Comparator<T> comparator)
static BigInteger	valueOfLehmerCode(int[] lehmer)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Lehmer

public Lehmer()

Method Details

lehmerValue

public static <T> BigInteger lehmerValue(Collection<T> items,
 Comparator<T> comparator)

lehmerCode

public static <T> int[] lehmerCode(Collection<T> items,
 Comparator<T> comparator)

For a given collection of unique items with a defined total ordering (via comparator) compute the natural number that correspends to n-th permutation w.r.t. the lehmer code. This implementation adds the provided items into a LinkedHashSet - so only their first occurrence matters.

Type Parameters:

T -

Parameters:

items -

comparator -

Returns:

valueOfLehmerCode

public static BigInteger valueOfLehmerCode(int[] lehmer)