+++ /dev/null
-/*
- * Copyright (c) 2003-2005 The BISON Project
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License version 2 as
- * published by the Free Software Foundation.
- *
- * This program 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 Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- *
- */
-
-package peersim.util;
-
-import java.util.NoSuchElementException;
-import java.util.Random;
-
-/**
-* This class provides a random permutation of indexes. Useful for
-* random sampling without replacement.
-*/
-public class RandPermutation implements IndexIterator {
-
-
-// ======================= private fields ============================
-// ===================================================================
-
-
-private int[] buffer = null;
-
-private int len = 0;
-
-private int pointer = 0;
-
-private final Random r;
-
-
-// ======================= initialization ============================
-// ===================================================================
-
-
-/** Sets source of randomness to be used. You need to call
-* {@link #reset} to fully initialize the object.
-* @param r Source of randomness
-*/
-public RandPermutation( Random r ) { this.r=r; }
-
-// -------------------------------------------------------------------
-
-/** Sets source of randomness and initial size. It calls
-* {@link #setPermutation} to fully initialize the object with a
-* permuation ready to use.
-* @param r Source of randomness
-* @param k size of permutation
-*/
-public RandPermutation( int k, Random r ) {
-
- this.r=r;
- setPermutation(k);
-}
-
-
-// ======================= public methods ============================
-// ===================================================================
-
-
-/**
-* It calculates a random permutation of the integers from 0 to k-1.
-* The permutation can be read using method {@link #get}.
-* If the previous permutation was of the same length, it is more efficient.
-* Note that after calling this the object is reset, so {@link #next} can
-* be called k times, even if {@link #get} was called an arbitrary number of
-* times. Note however that mixing {@link #get} and {@link #next} results in
-* incorrect behavior for {@link #get} (but {@link #next} works fine).
-* The idea is to use this method only in connection with {@link #get}.
-*/
-public void setPermutation(int k) {
-
- reset(k);
-
- for(int i=len; i>1; i--)
- {
- int j = r.nextInt(i);
- int a = buffer[j];
- buffer[j] = buffer[i-1];
- buffer[i-1] = a;
- }
-}
-
-// -------------------------------------------------------------------
-
-/**
-* Returns the ith element of the permutation set by {@link #setPermutation}.
-* If {@link #next} is called after {@link #setPermutation} and before
-* this method, then the behavior of this method is unspecified.
-*/
-public int get(int i) {
-
- if( i >= len ) throw new IndexOutOfBoundsException();
- return buffer[i];
-}
-
-// -------------------------------------------------------------------
-
-/**
-* It initiates a random permutation of the integers from 0 to k-1.
-* It does not actually calculate the permutation.
-* The permutation can be read using method {@link #next}.
-* Calls to {@link #get} return undefined values, so {@link #next} must be used.
-* If the previous permutation was of the same length, it is more efficient.
-*/
-public void reset(int k) {
-
- pointer = k;
- if( len == k ) return;
-
- if( buffer == null || buffer.length < k )
- {
- buffer = new int[k];
- }
-
- len = k;
- for( int i=0; i<len; ++i ) buffer[i]=i;
-}
-
-// -------------------------------------------------------------------
-
-/** Next random sample without replacement */
-public int next() {
-
- if( pointer < 1 ) throw new NoSuchElementException();
-
- int j = r.nextInt(pointer);
- int a = buffer[j];
- buffer[j] = buffer[pointer-1];
- buffer[pointer-1] = a;
-
- return buffer[--pointer];
-}
-
-// -------------------------------------------------------------------
-
-public boolean hasNext() { return pointer > 0; }
-
-// -------------------------------------------------------------------
-
-/*
-public static void main( String pars[] ) throws Exception {
-
- RandPermutation rp = new RandPermutation(new Random());
-
- int k;
-
- k = Integer.parseInt(pars[0]);
- rp.setPermutation(k);
- for(int i=0; i<k; ++i) System.out.println(rp.get(i));
-
- System.out.println();
-
- k = Integer.parseInt(pars[1]);
- rp.reset(k);
- while(rp.hasNext()) System.out.println(rp.next());
-
- System.out.println();
-
- k = Integer.parseInt(pars[2]);
- rp.reset(k);
- while(rp.hasNext()) System.out.println(rp.next());
- System.out.println(rp.next());
-}
-*/
-}
