001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math3.util;
018
019import java.io.Serializable;
020
021import org.apache.commons.math3.exception.MathIllegalArgumentException;
022import org.apache.commons.math3.random.RandomGenerator;
023
024
025/**
026 * A strategy of selecting random index between begin and end indices.
027 * @since 3.4
028 */
029public class RandomPivotingStrategy implements PivotingStrategyInterface, Serializable {
030
031    /** Serializable UID. */
032    private static final long serialVersionUID = 20140713L;
033
034    /** Random generator to use for selecting pivot. */
035    private final RandomGenerator random;
036
037    /** Simple constructor.
038     * @param random random generator to use for selecting pivot
039     */
040    public RandomPivotingStrategy(final RandomGenerator random) {
041        this.random = random;
042    }
043
044    /**
045     * {@inheritDoc}
046     * A uniform random pivot selection between begin and end indices
047     * @return The index corresponding to a random uniformly selected
048     * value between first and the last indices of the array slice
049     * @throws MathIllegalArgumentException when indices exceeds range
050     */
051    public int pivotIndex(final double[] work, final int begin, final int end)
052        throws MathIllegalArgumentException {
053        MathArrays.verifyValues(work, begin, end-begin);
054        return begin + random.nextInt(end - begin - 1);
055    }
056
057}