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Java example source code file (MedianOf3PivotingStrategy.java)

This example Java source code file (MedianOf3PivotingStrategy.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

mathillegalargumentexception, medianof3pivotingstrategy, pivotingstrategyinterface, serializable

The MedianOf3PivotingStrategy.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.io.Serializable;

import org.apache.commons.math3.exception.MathIllegalArgumentException;


/**
 * Classic median of 3 strategy given begin and end indices.
 * @since 3.4
 */
public class MedianOf3PivotingStrategy implements PivotingStrategyInterface, Serializable {

    /** Serializable UID. */
    private static final long serialVersionUID = 20140713L;

    /**{@inheritDoc}
     * This in specific makes use of median of 3 pivoting.
     * @return The index corresponding to a pivot chosen between the
     * first, middle and the last indices of the array slice
     * @throws MathIllegalArgumentException when indices exceeds range
     */
    public int pivotIndex(final double[] work, final int begin, final int end)
        throws MathIllegalArgumentException {
        MathArrays.verifyValues(work, begin, end-begin);
        final int inclusiveEnd = end - 1;
        final int middle = begin + (inclusiveEnd - begin) / 2;
        final double wBegin = work[begin];
        final double wMiddle = work[middle];
        final double wEnd = work[inclusiveEnd];

        if (wBegin < wMiddle) {
            if (wMiddle < wEnd) {
                return middle;
            } else {
                return wBegin < wEnd ? inclusiveEnd : begin;
            }
        } else {
            if (wBegin < wEnd) {
                return begin;
            } else {
                return wMiddle < wEnd ? inclusiveEnd : middle;
            }
        }
    }

}

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