Make all combinations of N size of objects - Java Data Structure

Java examples for Data Structure:Algorithm

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Description

Make all combinations of N size of objects

Demo Code

/*/*w ww  .ja va2  s . c om*/
 * Copyright (c) 2012 The Broad Institute
 * 
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
//package com.java2s;
import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

public class Main {
    /**
     * Make all combinations of N size of objects
     *
     * if objects = [A, B, C]
     * if N = 1 => [[A], [B], [C]]
     * if N = 2 => [[A, A], [B, A], [C, A], [A, B], [B, B], [C, B], [A, C], [B, C], [C, C]]
     *
     * @param objects
     * @param n
     * @param <T>
     * @param withReplacement if false, the resulting permutations will only contain unique objects from objects
     * @return
     */
    public static <T> List<List<T>> makePermutations(final List<T> objects,
            final int n, final boolean withReplacement) {
        final List<List<T>> combinations = new ArrayList<List<T>>();

        if (n <= 0)
            ;
        else if (n == 1) {
            for (final T o : objects)
                combinations.add(Collections.singletonList(o));
        } else {
            final List<List<T>> sub = makePermutations(objects, n - 1,
                    withReplacement);
            for (List<T> subI : sub) {
                for (final T a : objects) {
                    if (withReplacement || !subI.contains(a))
                        combinations.add(cons(a, subI));
                }
            }
        }

        return combinations;
    }

    public static <T> List<T> cons(final T elt, final List<T> l) {
        List<T> l2 = new ArrayList<T>();
        l2.add(elt);
        if (l != null)
            l2.addAll(l);
        return l2;
    }
}

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