/*
*
* 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();
}
}