Java List Select selectExactly(List original, int nb)

Description

select Exactly

License

Open Source License

Declaration

public static <E> Collection<List<E>> selectExactly(List<E> original, int nb) 

Method Source Code

//package com.java2s;
/* ========================================================================
 * PlantUML : a free UML diagram generator
 * ========================================================================
 *
 * (C) Copyright 2009, Arnaud Roques//ww  w .ja v  a  2  s.  c  om
 *
 * Project Info:  http://plantuml.sourceforge.net
 * 
 * This file is part of PlantUML.
 *
 * PlantUML is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * PlantUML 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 General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * Original Author:  Arnaud Roques
 * 
 * Revision $Revision: 3830 $
 *
 */

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

public class Main {
    public static <E> Collection<List<E>> selectExactly(List<E> original, int nb) {
        if (nb < 0) {
            throw new IllegalArgumentException();
        }
        if (nb == 0) {
            return Collections.emptyList();
        }
        if (nb == 1) {
            final List<List<E>> result = new ArrayList<List<E>>();
            for (E element : original) {
                result.add(Collections.singletonList(element));
            }
            return result;

        }
        if (nb > original.size()) {
            return Collections.emptyList();
        }
        if (nb == original.size()) {
            return Collections.singletonList(original);
        }
        final List<List<E>> result = new ArrayList<List<E>>();

        for (List<E> subList : selectExactly(original.subList(1, original.size()), nb - 1)) {
            final List<E> newList = new ArrayList<E>();
            newList.add(original.get(0));
            newList.addAll(subList);
            result.add(Collections.unmodifiableList(newList));
        }
        result.addAll(selectExactly(original.subList(1, original.size()), nb));

        return Collections.unmodifiableList(result);
    }
}

Related

1. select(List list, List indices, List sel)
2. select(List src, List indexes)
3. selectDuplicateQualifiers( List elements)
4. selectElements(final List list, int start, int end)
5. selectFields(String[] fields, List fieldList, int allFieldsFrom, String separator)
6. selectRandom(List list)
7. selectTopN(List originalList, int topN, Comparator