Java Array Shuffle shuffle(Object[] a)

Description

Rearrange the elements of an array in random order.

License

Open Source License

Declaration

public static void shuffle(Object[] a) 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.util.Random;

public class Main {
    private static Random random;

    /**//from   w  w  w .  j av  a  2s  . c o  m
     * Rearrange the elements of an array in random order.
     */
    public static void shuffle(Object[] a) {
        int N = a.length;
        for (int i = 0; i < N; i++) {
            int r = i + uniform(N - i); // between i and N-1
            Object temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Rearrange the elements of a double array in random order.
     */
    public static void shuffle(double[] a) {
        int N = a.length;
        for (int i = 0; i < N; i++) {
            int r = i + uniform(N - i); // between i and N-1
            double temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Rearrange the elements of an int array in random order.
     */
    public static void shuffle(int[] a) {
        int N = a.length;
        for (int i = 0; i < N; i++) {
            int r = i + uniform(N - i); // between i and N-1
            int temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Rearrange the elements of the subarray a[lo..hi] in random order.
     */
    public static void shuffle(Object[] a, int lo, int hi) {
        if (lo < 0 || lo > hi || hi >= a.length) {
            throw new IndexOutOfBoundsException("Illegal subarray range");
        }
        for (int i = lo; i <= hi; i++) {
            int r = i + uniform(hi - i + 1); // between i and hi
            Object temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Rearrange the elements of the subarray a[lo..hi] in random order.
     */
    public static void shuffle(double[] a, int lo, int hi) {
        if (lo < 0 || lo > hi || hi >= a.length) {
            throw new IndexOutOfBoundsException("Illegal subarray range");
        }
        for (int i = lo; i <= hi; i++) {
            int r = i + uniform(hi - i + 1); // between i and hi
            double temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Rearrange the elements of the subarray a[lo..hi] in random order.
     */
    public static void shuffle(int[] a, int lo, int hi) {
        if (lo < 0 || lo > hi || hi >= a.length) {
            throw new IndexOutOfBoundsException("Illegal subarray range");
        }
        for (int i = lo; i <= hi; i++) {
            int r = i + uniform(hi - i + 1); // between i and hi
            int temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }

    /**
     * Return real number uniformly in [0, 1).
     */
    public static double uniform() {
        return random.nextDouble();
    }

    /**
     * Returns an integer uniformly between 0 (inclusive) and N (exclusive).
     * @throws IllegalArgumentException if <tt>N <= 0</tt>
     */
    public static int uniform(int N) {
        if (N <= 0)
            throw new IllegalArgumentException("Parameter N must be positive");
        return random.nextInt(N);
    }

    /**
     * Returns an integer uniformly in [a, b).
     * @throws IllegalArgumentException if <tt>b <= a</tt>
     * @throws IllegalArgumentException if <tt>b - a >= Integer.MAX_VALUE</tt>
     */
    public static int uniform(int a, int b) {
        if (b <= a)
            throw new IllegalArgumentException("Invalid range");
        if ((long) b - a >= Integer.MAX_VALUE)
            throw new IllegalArgumentException("Invalid range");
        return a + uniform(b - a);
    }

    /**
     * Returns a real number uniformly in [a, b).
     * @throws IllegalArgumentException unless <tt>a < b</tt>
     */
    public static double uniform(double a, double b) {
        if (!(a < b))
            throw new IllegalArgumentException("Invalid range");
        return a + uniform() * (b - a);
    }
}

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