| /* |
| * |
| * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * - Neither the name of Oracle nor the names of its |
| * contributors may be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
| * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
| * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR |
| * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
| * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING |
| * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
| * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| |
| |
| import java.util.Random; |
| |
| /** |
| * An object that implements a cheesy pseudorandom permutation of the integers |
| * from zero to some user-specified value. (The permutation is a linear |
| * function.) |
| * |
| * @author Josh Bloch |
| */ |
| class Permuter { |
| /** |
| * The size of the permutation. |
| */ |
| private int modulus; |
| |
| /** |
| * Nonnegative integer less than n that is relatively prime to m. |
| */ |
| private int multiplier; |
| |
| /** |
| * Pseudorandom nonnegative integer less than n. |
| */ |
| private int addend = 22; |
| |
| public Permuter(int n) { |
| if (n<0) { |
| throw new IllegalArgumentException(); |
| } |
| modulus = n; |
| if (n==1) { |
| return; |
| } |
| |
| // Initialize the multiplier and offset |
| multiplier = (int) Math.sqrt(n); |
| while (gcd(multiplier, n) != 1) { |
| if (++multiplier == n) { |
| multiplier = 1; |
| } |
| } |
| } |
| |
| /** |
| * Returns the integer to which this permuter maps the specified integer. |
| * The specified integer must be between 0 and n-1, and the returned |
| * integer will be as well. |
| */ |
| public int map(int i) { |
| return (multiplier * i + addend) % modulus; |
| } |
| |
| /** |
| * Calculate GCD of a and b, which are assumed to be non-negative. |
| */ |
| private static int gcd(int a, int b) { |
| while(b != 0) { |
| int tmp = a % b; |
| a = b; |
| b = tmp; |
| } |
| return a; |
| } |
| |
| /** |
| * Simple test. Takes modulus on command line and prints out permutation. |
| */ |
| public static void main(String[] args) { |
| int modulus = Integer.parseInt(args[0]); |
| Permuter p = new Permuter(modulus); |
| for (int i=0; i<modulus; i++) { |
| System.out.print(p.map(i)+" "); |
| } |
| System.out.println(); |
| } |
| } |