Main.java Source code

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Here is the source code for Main.java

Source

//package com.java2s;
/*
 * Copyright The Codehaus Foundation.
 *
 * Licensed 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.
 */

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;

import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

public class Main {
    /**
     * Returns a {@link Collection} containing the intersection
     * of the given {@link Collection}s.
     * <p>
     * The cardinality of each element in the returned {@link Collection}
     * will be equal to the minimum of the cardinality of that element
     * in the two given {@link Collection}s.
     *
     * @param a The first collection
     * @param b The second collection
     * @see Collection#retainAll
     * @return  The intersection of a and b, never null
     */
    public static <E> Collection<E> intersection(final Collection<E> a, final Collection<E> b) {
        ArrayList<E> list = new ArrayList<E>();
        Map<E, Integer> mapa = getCardinalityMap(a);
        Map<E, Integer> mapb = getCardinalityMap(b);
        Set<E> elts = new HashSet<E>(a);
        elts.addAll(b);
        for (E obj : elts) {
            for (int i = 0, m = Math.min(getFreq(obj, mapa), getFreq(obj, mapb)); i < m; i++) {
                list.add(obj);
            }
        }
        return list;
    }

    /**
     * Returns a {@link Map} mapping each unique element in
     * the given {@link Collection} to an {@link Integer}
     * representing the number of occurances of that element
     * in the {@link Collection}.
     * An entry that maps to <tt>null</tt> indicates that the
     * element does not appear in the given {@link Collection}.
     * @param col The collection to count cardinalities for
     * @return A map of counts, indexed on each element in the collection
     */
    public static <E> Map<E, Integer> getCardinalityMap(final Collection<E> col) {
        HashMap<E, Integer> count = new HashMap<E, Integer>();
        for (E obj : col) {
            Integer c = count.get(obj);
            if (null == c) {
                count.put(obj, 1);
            } else {
                count.put(obj, c + 1);
            }
        }
        return count;
    }

    private static <E> int getFreq(final E obj, final Map<E, Integer> freqMap) {
        try {
            Integer o = freqMap.get(obj);
            if (o != null) // minimize NullPointerExceptions
            {
                return o;
            }
        } catch (NullPointerException ignore) {
        } catch (NoSuchElementException ignore) {
        }
        return 0;
    }
}