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/*
* File: Combinations.java
* Authors: Kevin R. Dixon
* Company: Sandia National Laboratories
* Project: Cognitive Foundry
*
* Copyright Dec 11, 2012, Sandia Corporation.
* Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
* license for use of this work by or on behalf of the U.S. Government.
* Export of this program may require a license from the United States
* Government. See CopyrightHistory.txt for complete details.
*
*/
package gov.sandia.cognition.math;
import gov.sandia.cognition.math.matrix.Vector;
import gov.sandia.cognition.math.matrix.VectorFactory;
import gov.sandia.cognition.util.AbstractCloneableSerializable;
import gov.sandia.cognition.util.ArgumentChecker;
import gov.sandia.cognition.util.CloneableSerializable;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
/**
* Enumerates all the combinations on a given number of items sampled from a
* larger set without considering order, that is, (1,2) is the same as (2,1).
* For example, there are 3 ways to choose 2 objects from a set of 3:
* (1,2), (1,3), (2,3).
* @author Kevin R. Dixon
* @since 3.4.2
*/
public class Combinations
extends AbstractSet
implements CloneableSerializable
{
/**
* Universe set size
*/
private int N;
/**
* Number of objects to choose from the universe set.
*/
private int k;
/**
* Creates a new instance of Combinations
* @param N
* Universe set size
* @param k
* Number of objects to choose from the universe set.
*/
public Combinations(
int N,
int k )
{
ArgumentChecker.assertIsPositive("N", N );
ArgumentChecker.assertIsNonNegative("k", k );
ArgumentChecker.assertIsInRangeInclusive("0<=k<=N", k, 0, N);
this.N = N;
this.k = k;
}
@Override
public Combinations clone()
{
try
{
return (Combinations) super.clone();
}
catch (CloneNotSupportedException ex)
{
throw new RuntimeException(ex);
}
}
@Override
public Iterator iterator()
{
return new IndexIterator(this.N, this.k);
}
@Override
public int size()
{
return MathUtil.binomialCoefficient(N, k);
}
/**
* Getter for N
* @return
* Universe set size
*/
public int getN()
{
return this.N;
}
/**
* Getter for k
* @return the k
* Number of objects to choose from the universe set.
*/
public int getK()
{
return this.k;
}
/**
* Partial implementation of a CombinationsIterator.
* @param
* Type of iterator given by the implementing subclass
* @param
* Type of parameter returned by the next() method.
*/
protected abstract static class AbstractCombinationsIterator, ClassType>
extends AbstractCloneableSerializable
implements Iterator
{
/**
* Universe set size
*/
protected int N;
/**
* Number of objects to choose from the universe set.
*/
protected int k;
/**
*
*/
protected int size;
/**
* Index into the universal set.
*/
protected int index;
/**
* Child iterator for recursion
*/
protected IteratorType child;
/**
* Creates a new instance of AbstractCombinationsIterator
* @param N
* Universe set size
* @param k
* Number of objects to choose from the universe set.
*/
public AbstractCombinationsIterator(
int N,
int k )
{
ArgumentChecker.assertIsPositive("N", N);
ArgumentChecker.assertIsNonNegative("k", k);
ArgumentChecker.assertIsNonNegative("N-k", N-k);
this.N = N;
this.k = k;
this.size = MathUtil.binomialCoefficient(N, k);
this.index = 0;
}
@Override
public boolean hasNext()
{
return this.index < this.size;
}
@Override
public void remove()
{
throw new UnsupportedOperationException("Not supported yet.");
}
}
/**
* Iterator that returns the index into a set: 0, 1, 2, ... N.
*/
public class IndexIterator
extends AbstractCombinationsIterator
{
/**
* Value to return
*/
private double value = -1.0;
/**
* Creates a new instance of IndexIterator
* @param N
* Universe set size
* @param k
*/
public IndexIterator(
int N,
int k)
{
super( N, k );
this.value = 1.0;
if( (k > 0) && (N > k) )
{
this.child = new IndexIterator(N-1, k-1);
}
}
@Override
public Vector next()
{
this.index++;
Vector retval;
if( this.k == 0 )
{
retval = VectorFactory.getDefault().createVector(this.N);
}
else if( this.k == this.N )
{
retval = VectorFactory.getDefault().createVector(this.N, 1.0);
}
else
{
Vector subvector;
if( this.child.hasNext() )
{
subvector = this.child.next();
}
else if( this.value == 1.0 )
{
this.value = 0.0;
this.child = new IndexIterator(this.N-1, this.k);
subvector = this.child.next();
}
else
{
throw new IllegalArgumentException( "Nothing left: index = " + this.index + ", size = " + this.size );
}
retval = VectorFactory.getDefault().createVector(this.N);
retval.setElement(0, this.value);
for( int i = 1; i < retval.getDimensionality(); i++ )
{
retval.setElement(i, subvector.getElement(i-1));
}
}
return retval;
}
}
/**
* Creates a new instance of SubsetIterator, one that returns the elements
* from a given set
* @param
* Class type of the subset
*/
public static class SubsetIterator
extends AbstractCombinationsIterator, LinkedList>
{
/**
* Universal set into which to index.
*/
private ArrayList set;
/**
* Flag to include the current element
*/
private boolean include;
/**
* Base index into the universal set from which we recursed
*/
private int baseIndex;
/**
* Creates a new instance of SubsetIterator
* @param N
* Universe set size
* @param k
* Number of objects to choose from the universe set.
* @param set
* Universal set into which to index.
*/
public SubsetIterator(
int N,
int k,
ArrayList set )
{
this( N, k, set, 0 );
}
/**
* Creates a new instance of SubsetIterator
* @param N
* Universe set size
* @param k
* Number of objects to choose from the universe set.
* @param set
* Universal set into which to index.
* @param baseIndex
* Base index into the universal set from which we recursed
*/
private SubsetIterator(
int N,
int k,
ArrayList set,
int baseIndex )
{
super( N, k );
this.include = true;
this.baseIndex = baseIndex;
this.set = set;
if( (k > 0) && (N > k) )
{
this.child = new SubsetIterator(
this.N-1, this.k-1, this.set, this.baseIndex+1);
}
}
@Override
public LinkedList next()
{
this.index++;
LinkedList retval = new LinkedList();
if( this.k == 0 )
{
}
else if( this.k == this.N )
{
retval.addAll( this.set.subList(this.baseIndex,this.set.size()));
}
else
{
LinkedList sublist;
if( this.child.hasNext() )
{
sublist = this.child.next();
}
else if( this.include )
{
this.include = false;
this.child = new SubsetIterator(
this.N-1, this.k, this.set, this.baseIndex+1);
sublist = this.child.next();
}
else
{
throw new IllegalArgumentException( "Nothing left: index = " + this.index + ", size = " + this.size );
}
if( this.include )
{
retval.add( this.set.get(this.baseIndex) );
}
retval.addAll( sublist );
}
return retval;
}
}
}
