com.diversityarrays.util.CombinationsAndPermutations.java Source code

Introduction

Here is the source code for com.diversityarrays.util.CombinationsAndPermutations.java

Source

/*
KDXplore provides KDDart Data Exploration and Management
Copyright (C) 2015,2016,2017  Diversity Arrays Technology, Pty Ltd.
    
KDXplore may be redistributed and may be modified 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.
    
KDXplore 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 KDXplore.  If not, see <http://www.gnu.org/licenses/>.
*/
package com.diversityarrays.util;

import java.util.Arrays;

import org.apache.commons.collections15.Closure;

public class CombinationsAndPermutations {

    static public <T> void combinations(T[] names, int nPerCombination, Closure<T[]> collector) {
        T[] namesBeforeNameIndex = Arrays.copyOf(names, nPerCombination);

        for (int i = 0; i < names.length; ++i) {
            namesBeforeNameIndex[0] = names[i];
            combinations(namesBeforeNameIndex, 1, names, i + 1, collector);
        }
    }

    static private <T> void combinations(T[] namesBeforeNameIndex, int fillIndex, T[] names, int nameIndex,
            Closure<T[]> collector) {
        if (fillIndex >= namesBeforeNameIndex.length) {
            collector.execute(namesBeforeNameIndex);
        } else {
            int nNames = names.length;
            for (int i = nameIndex; i < nNames; ++i) {
                namesBeforeNameIndex[fillIndex] = names[i];
                combinations(namesBeforeNameIndex, fillIndex + 1, names, i + 1, collector);
            }
            namesBeforeNameIndex[fillIndex] = null;
        }
    }

    /*
    procedure generate(n : integer, A : array of any):
     if n = 1 then
      output(A)
     else
    for i := 1; i  n; i += 1 do
        generate(n - 1, A)
        if n is odd then
            j ? 1
        else
            j ? i
        swap(A[j], A[n])
     */

    static public <T> void permutations(T[] names, Closure<T[]> collector) {
        permutations(names.length, names, collector);
    }

    static private <T> void permutations(int nNames, T[] names, Closure<T[]> collector) {
        if (nNames == 1) {
            collector.execute(names);
        } else {
            for (int i = 1; i <= nNames; ++i) {
                permutations(nNames - 1, names, collector);
                int jj = (1 == (nNames & 1)) ? 1 : i;

                int j = jj - 1;

                T tmp = names[j];
                names[j] = names[nNames - 1];
                names[nNames - 1] = tmp;
                //            collector.execute(names);
            }
        }
    }

    private CombinationsAndPermutations() {
    }
}