Java Array Shuffle shuffle(T[] a, int from, int to, Random rnd)

Description

Randomly permute the specified array from using the specified source of randomness.

License

Apache License

Parameter

Parameter	Description
a	the array to be shuffled.
from	the initial index of the range to be shuffled, inclusive
to	the final index of the range to be shuffled, exclusive.
rnd	the source of randomness to use to shuffle the list.

Declaration

public static <T> T[] shuffle(T[] a, int from, int to, Random rnd) 

Method Source Code

//package com.java2s;
/*//from  www  .j  a  va2s .  c om
 * Copyright (c) 2008 Kasper Nielsen.
 *
 * 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.Random;

public class Main {
    /**
     * Randomly permute the specified array from using the specified source of randomness. All permutations occur with
     * equal likelihood assuming that the source of randomness is fair.
     * <p>
     * This implementation traverses the array backwards, from the to index up to the from + 1 index, repeatedly
     * swapping a randomly selected element into the "current position". Elements are randomly selected from the portion
     * of the array that runs from the from index to the current position, inclusive.
     * <p>
     * This method runs in linear time.
     * 
     * @param a
     *            the array to be shuffled.
     * @param from
     *            the initial index of the range to be shuffled, inclusive
     * @param to
     *            the final index of the range to be shuffled, exclusive.
     * @param rnd
     *            the source of randomness to use to shuffle the list.
     */
    public static <T> T[] shuffle(T[] a, int from, int to, Random rnd) {
        for (int i = to; i > from + 1; i--) {
            swap(a, i - 1, rnd.nextInt(i - from) + from);
        }
        return a;
    }

    /** Swaps the two specified elements in the specified array. */
    static void swap(Object[] a, int i, int j) {
        Object o = a[i];
        a[i] = a[j];
        a[j] = o;
    }
}

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