Module org.cicirello.jpt

Package org.cicirello.permutations.distance

Class BlockInterchangeDistance

java.lang.Object

org.cicirello.permutations.distance.BlockInterchangeDistance

All Implemented Interfaces:

NormalizedPermutationDistanceMeasurer, NormalizedPermutationDistanceMeasurerDouble, PermutationDistanceMeasurer, PermutationDistanceMeasurerDouble

public class BlockInterchangeDistance
extends Object
implements NormalizedPermutationDistanceMeasurer

Block Interchange Distance is the minimum number of block interchanges necessary to transform one permutation into the other. A block interchange is an edit operation that takes two non-overlapping blocks (i.e., subsequence) and exchanges their locations in the permutation. For example, the permutation p1 = [0, 1, 2, 3, 4, 5, 6, 7] and p2 = [5, 6, 3, 4, 0, 1, 2, 7] is a block interchange distance of 1 since you can transform p2 into p1 by exchanging the blocks [5, 6] and [0, 1, 2] within p2.

Interchange distance is computed efficiently using the algorithm described in the article: D.A. Christie, "Sorting permutations by block-interchanges," Information Processing Letters, vol 60, pages 165-169, 1996.

Runtime: O(n), where n is the permutation length.

Constructor Summary

Constructors

Constructor	Description
BlockInterchangeDistance()	Constructs the distance measurer as specified in the class documentation.

Method Summary

Modifier and Type	Method	Description
int	distance(Permutation p1, Permutation p2)	Measures the distance between two permutations.
int	max(int length)	Computes the maximum possible distance between permutations of a specified length.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.cicirello.permutations.distance.NormalizedPermutationDistanceMeasurer

maxf, normalizedDistance

Methods inherited from interface org.cicirello.permutations.distance.PermutationDistanceMeasurer

distancef

Constructor Details

BlockInterchangeDistance

public BlockInterchangeDistance()

Constructs the distance measurer as specified in the class documentation.

Method Details

distance

public int distance(Permutation p1,
 Permutation p2)

Measures the distance between two permutations.

Specified by:

distance in interface PermutationDistanceMeasurer

Parameters:

p1 - first permutation

p2 - second permutation

Returns:

distance between p1 and p2

Throws:

IllegalArgumentException - if p1.length() is not equal to p2.length().

max

public int max(int length)

Description copied from interface: NormalizedPermutationDistanceMeasurer

Computes the maximum possible distance between permutations of a specified length.

Specified by:

max in interface NormalizedPermutationDistanceMeasurer

Parameters:

length - Permutation length.

Returns:

the maximum distance between a pair of permutations of the specified length.