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Java example source code file (CombinationsTest.java)

This example Java source code file (CombinationsTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

combinations, combinationstest, comparator, iterator, mathillegalargumentexception, test, util

The CombinationsTest.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math3.util;

import java.util.Iterator;
import java.util.Comparator;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.OutOfRangeException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.junit.Assert;
import org.junit.Test;

/**
 * Tests for the {@link Combinations} class.
 *
 */
public class CombinationsTest {
    @Test
    public void testAccessor1() {
        final int n = 5;
        final int k = 3;
        Assert.assertEquals(n, new Combinations(n, k).getN());
    }
    @Test
    public void testAccessor2() {
        final int n = 5;
        final int k = 3;
        Assert.assertEquals(k, new Combinations(n, k).getK());
    }

    @Test
    public void testLexicographicIterator() {
        checkLexicographicIterator(new Combinations(5, 3));
        checkLexicographicIterator(new Combinations(6, 4));
        checkLexicographicIterator(new Combinations(8, 2));
        checkLexicographicIterator(new Combinations(6, 1));
        checkLexicographicIterator(new Combinations(3, 3));
        checkLexicographicIterator(new Combinations(1, 1));
        checkLexicographicIterator(new Combinations(1, 0));
        checkLexicographicIterator(new Combinations(0, 0));
        checkLexicographicIterator(new Combinations(4, 2));
        checkLexicographicIterator(new Combinations(123, 2));
    }

    @Test(expected=DimensionMismatchException.class)
    public void testLexicographicComparatorWrongIterate1() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        comp.compare(new int[] {1}, new int[] {0, 1, 2});
    }

    @Test(expected=DimensionMismatchException.class)
    public void testLexicographicComparatorWrongIterate2() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        comp.compare(new int[] {0, 1, 2}, new int[] {0, 1, 2, 3});
    }

    @Test(expected=OutOfRangeException.class)
    public void testLexicographicComparatorWrongIterate3() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        comp.compare(new int[] {1, 2, 5}, new int[] {0, 1, 2});
    }

    @Test(expected=OutOfRangeException.class)
    public void testLexicographicComparatorWrongIterate4() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        comp.compare(new int[] {1, 2, 4}, new int[] {-1, 1, 2});
    }

    @Test
    public void testLexicographicComparator() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        Assert.assertEquals(1, comp.compare(new int[] {1, 2, 4},
                                            new int[] {1, 2, 3}));
        Assert.assertEquals(-1, comp.compare(new int[] {0, 1, 4},
                                             new int[] {0, 2, 4}));
        Assert.assertEquals(0, comp.compare(new int[] {1, 3, 4},
                                            new int[] {1, 3, 4}));
    }

    /**
     * Check that iterates can be passed unsorted.
     */
    @Test
    public void testLexicographicComparatorUnsorted() {
        final int n = 5;
        final int k = 3;
        final Comparator<int[]> comp = new Combinations(n, k).comparator();
        Assert.assertEquals(1, comp.compare(new int[] {1, 4, 2},
                                            new int[] {1, 3, 2}));
        Assert.assertEquals(-1, comp.compare(new int[] {0, 4, 1},
                                             new int[] {0, 4, 2}));
        Assert.assertEquals(0, comp.compare(new int[] {1, 4, 3},
                                            new int[] {1, 3, 4}));
    }

    @Test
    public void testEmptyCombination() {
        final Iterator<int[]> iter = new Combinations(12345, 0).iterator();
        Assert.assertTrue(iter.hasNext());
        final int[] c = iter.next();
        Assert.assertEquals(0, c.length);
        Assert.assertFalse(iter.hasNext());
    }

    @Test
    public void testFullSetCombination() {
        final int n = 67;
        final Iterator<int[]> iter = new Combinations(n, n).iterator();
        Assert.assertTrue(iter.hasNext());
        final int[] c = iter.next();
        Assert.assertEquals(n, c.length);

        for (int i = 0; i < n; i++) {
            Assert.assertEquals(i, c[i]);
        }

        Assert.assertFalse(iter.hasNext());
    }

    /**
     * Verifies that the iterator generates a lexicographically
     * increasing sequence of b(n,k) arrays, each having length k
     * and each array itself increasing.
     *
     * @param c Combinations.
     */
    private void checkLexicographicIterator(Combinations c) {
        final Comparator<int[]> comp = c.comparator();
        final int n = c.getN();
        final int k = c.getK();

        int[] lastIterate = null;

        long numIterates = 0;
        for (int[] iterate : c) {
            Assert.assertEquals(k, iterate.length);

            // Check that the sequence of iterates is ordered.
            if (lastIterate != null) {
                Assert.assertTrue(comp.compare(iterate, lastIterate) == 1);
            }

            // Check that each iterate is ordered.
            for (int i = 1; i < iterate.length; i++) {
                Assert.assertTrue(iterate[i] > iterate[i - 1]);
            }

            lastIterate = iterate;
            ++numIterates;
        }

        // Check the number of iterates.
        Assert.assertEquals(CombinatoricsUtils.binomialCoefficient(n, k),
                            numIterates);
    }

    @Test
    public void testCombinationsIteratorFail() {
        try {
            new Combinations(4, 5).iterator();
            Assert.fail("expecting MathIllegalArgumentException");
        } catch (MathIllegalArgumentException ex) {
            // ignored
        }

        try {
            new Combinations(-1, -2).iterator();
            Assert.fail("expecting MathIllegalArgumentException");
        } catch (MathIllegalArgumentException ex) {
            // ignored
        }
    }
}

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