cartesian product of arbitrary sets - Java java.util

Java examples for java.util:Set Operation

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Description

cartesian product of arbitrary sets

Demo Code

/* /*w  w  w .  ja v a 2s.  co  m*/
 * (c) 2008- RANDI2 Core Development Team
 * 
 * This file is part of RANDI2.
 * 
 * RANDI2 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.
 * 
 * RANDI2 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 General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along with
 * RANDI2. If not, see <http://www.gnu.org/licenses/>.
 */
//package com.java2s;
import java.util.HashSet;
import java.util.Set;

public class Main {
    /**
     * from http://stackoverflow.com/questions/714108/cartesian-product-of-arbitrary-sets-in-java
     * @param sets
     * @return
     */
    public static <E> Set<Set<E>> cartesianProduct(Set<E>... sets) {
        if (sets.length < 2)
            throw new IllegalArgumentException(
                    "Can't have a product of fewer than two sets (got "
                            + sets.length + ")");

        return _cartesianProduct(0, sets);
    }

    private static <E> Set<Set<E>> _cartesianProduct(int index,
            Set<E>... sets) {
        Set<Set<E>> ret = new HashSet<Set<E>>();
        if (index == sets.length) {
            ret.add(new HashSet<E>());
        } else {
            for (E obj : sets[index]) {
                for (Set<E> set : _cartesianProduct(index + 1, sets)) {
                    set.add(obj);
                    ret.add(set);
                }
            }
        }
        return ret;
    }
}

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