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