Java Random Number getRandomNumbers(int range, int count, Random rnd)

Description

get Random Numbers

License

Open Source License

Declaration

public static ArrayList<Integer> getRandomNumbers(int range, int count, Random rnd) 

Method Source Code

//package com.java2s;
/* /*w w  w  .  ja  va 2 s.c  om*/
 * Copyright 2008-2013, ETH Z?rich, Samuel Welten, Michael Kuhn, Tobias Langner,
 * Sandro Affentranger, Lukas Bossard, Michael Grob, Rahul Jain, 
 * Dominic Langenegger, Sonia Mayor Alonso, Roger Odermatt, Tobias Schlueter,
 * Yannick Stucki, Sebastian Wendland, Samuel Zehnder, Samuel Zihlmann,       
 * Samuel Zweifel
 *
 * This file is part of Jukefox.
 *
 * Jukefox is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software 
 * Foundation, either version 3 of the License, or any later version. Jukefox is
 * distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; 
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 
 * PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * Jukefox. If not, see <http://www.gnu.org/licenses/>.
 */

import java.util.ArrayList;
import java.util.HashMap;

import java.util.Random;

public class Main {
    public static ArrayList<Integer> getRandomNumbers(int range, int count, Random rnd) {
        //      long t1 = System.currentTimeMillis();
        if (count > range) {
            return null;
        }
        if (count < 0 || range < 0) {
            return null;
        }
        ArrayList<Integer> indices = new ArrayList<Integer>();
        if (count < range / 2) {
            HashMap<Integer, Integer> used = new HashMap<Integer, Integer>();
            int n = range;
            while (indices.size() < count) {
                Integer r = Integer.valueOf(rnd.nextInt(n));
                if (used.containsKey(r)) {
                    indices.add(used.get(r));
                } else {
                    indices.add(r);
                }
                addToUsed(used, r, n - 1);
                n--;
            }
        } else {

            ArrayList<Integer> unused = new ArrayList<Integer>(range);
            for (int i = 0; i < range; i++) {
                //            Log.v(TAG, "TT" + i + " " + (System.currentTimeMillis() - t1));
                unused.add(i);
            }
            int u = 0;
            while (indices.size() < count) {
                //            Log.v(TAG, "TD" + u + " " + (System.currentTimeMillis() - t1));
                Integer r = unused.remove(rnd.nextInt(unused.size()));
                indices.add(r);
                u++;
            }
        }
        return indices;
    }

    private static void addToUsed(HashMap<Integer, Integer> used, Integer key, Integer value) {
        if (used.containsKey(value)) {
            value = used.get(value);
            addToUsed(used, key, value);
        }
        used.put(key, value);
    }
}

Related

1. getRandomNumber(int startNumber, int endNumber)
2. getRandomNumberBetween(int min, int max)
3. getRandomNumberFixLength()
4. getRandomNumberGenerator()
5. getRandomNumberInRange(Random random, int min, int max)
6. getRandomNumberString(int length)
7. getRandomNumer(int length)
8. getRandomNumericString(int maxlen)
9. getRandomPortNumber()