com.hfg.math.Combinations Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of com_hfg Show documentation
Show all versions of com_hfg Show documentation
com.hfg xml, html, svg, and bioinformatics utility library
package com.hfg.math;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import com.hfg.util.collection.CollectionUtil;
//------------------------------------------------------------------------------
/**
Generate combinations of the specified size using the specified list of objects.
A combination is a set of objects in which position (or order) is NOT important.
@author J. Alex Taylor, hairyfatguy.com
*/
//------------------------------------------------------------------------------
// com.hfg Library
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
//
// J. Alex Taylor, President, Founder, CEO, COO, CFO, OOPS hairyfatguy.com
// [email protected]
//------------------------------------------------------------------------------
public class Combinations
{
//---------------------------------------------------------------------------
public static> List> combinations(List inObjects, int inCombinationSize)
{
List> combinations = null;
if (CollectionUtil.hasValues(inObjects))
{
if (inCombinationSize == 1)
{
combinations = new ArrayList<>(inObjects.size());
for (T obj : inObjects)
{
combinations.add(Collections.singletonList(obj));
}
}
else
{
combinations = new ArrayList<>();
for (int i = 0; i <= inObjects.size() - inCombinationSize; i++)
{
T firstItem = inObjects.get(i);
List> additionalItems = combinations(inObjects.subList(i + 1, inObjects.size()), inCombinationSize - 1);
for (List additional : additionalItems)
{
List combination = new ArrayList<>();
combination.add(firstItem);
combination.addAll(additional);
combinations.add(combination);
}
}
}
}
return combinations;
}
//---------------------------------------------------------------------------
public static int countOfCombinationsWithRepetition(List inObjects, int inCombinationSize)
{
int numCombinations = 0;
if (CollectionUtil.hasValues(inObjects))
{
if (inCombinationSize == 1)
{
// Special case if combination size is 1
numCombinations = inObjects.size();
}
else
{
int numeratorFactorial = inObjects.size() + inCombinationSize - 1; // (n + r - 1)!
int denominatorFactorial = inObjects.size() - 1; // (n - 1)!
long factorialDivisionResult = 1;
for (int i = denominatorFactorial + 1; i <= numeratorFactorial; i++)
{
factorialDivisionResult *= i;
}
numCombinations = (int) (factorialDivisionResult / MathUtil.factorial(inCombinationSize));
}
}
return numCombinations;
}
//---------------------------------------------------------------------------
public static> List combinationsWithRepetition(List inObjects, int inCombinationSize)
{
List combinations = null;
if (CollectionUtil.hasValues(inObjects))
{
if (inCombinationSize == 1)
{
// Special case if combination size is 1
combinations = new ArrayList<>(inObjects.size());
for (T obj : inObjects)
{
T[] combination = (T[]) Array.newInstance(inObjects.get(0).getClass(), inCombinationSize);
combination[0] = obj;
combinations.add(combination);
}
}
else
{
int numeratorFactorial = inObjects.size() + inCombinationSize - 1; // (n + r - 1)!
int denominatorFactorial = inObjects.size() - 1; // (n - 1)!
long factorialDivisionResult = 1;
for (int i = denominatorFactorial + 1; i <= numeratorFactorial; i++)
{
factorialDivisionResult *= i;
}
int numCombinations = (int) (factorialDivisionResult / MathUtil.factorial(inCombinationSize));
combinations = new ArrayList<>(numCombinations);
innerCombinationWithRepetition(inObjects, (T[]) Array.newInstance(inObjects.get(0).getClass(), inCombinationSize), 0, inCombinationSize, 0, inObjects.size() - 1, combinations);
}
}
return combinations;
}
//---------------------------------------------------------------------------
private static > void innerCombinationWithRepetition(List inObjects, T[] inChosen,
int inIndex, int inCombinationSize, int inStartIdx, int inEndIdx, List inCombinations)
{
// Since index has become r, current combination is ready to be printed, print
if (inIndex == inCombinationSize)
{
inCombinations.add(inChosen.clone());
}
else
{
// One by one choose all elements (without considering
// the fact whether element is already chosen or not)
// and recur
for (int i = inStartIdx; i <= inEndIdx; i++)
{
inChosen[inIndex] = inObjects.get(i);
innerCombinationWithRepetition(inObjects, inChosen, inIndex + 1, inCombinationSize, i, inEndIdx, inCombinations);
}
}
}
}