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source: trunk/sources/HeuristicLab.Random/3.3/RandomEnumerable.cs @ 6254

Last change on this file since 6254 was 5809, checked in by mkommend, 14 years ago

#1418: Reintegrated branch into trunk.

File size: 1.9 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2011 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
4 *
5 * This file is part of HeuristicLab.
6 *
7 * HeuristicLab is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
11 *
12 * HeuristicLab is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
19 */
20#endregion
21
22using System;
23using System.Collections.Generic;
24
25namespace HeuristicLab.Random {
26  public class RandomEnumerable {
27    public static IEnumerable<int> SampleRandomNumbers(int maxElement, int count) {
28      return SampleRandomNumbers(Environment.TickCount, 0, maxElement, count);
29    }
30
31    public static IEnumerable<int> SampleRandomNumbers(int start, int end, int count) {
32      return SampleRandomNumbers(Environment.TickCount, start, end, count);
33    }
34
35    //algorithm taken from progamming pearls page 127
36    //IMPORTANT because IEnumerables with yield are used the seed must best be specified to return always
37    //the same sequence of numbers without caching the values.
38    public static IEnumerable<int> SampleRandomNumbers(int seed, int start, int end, int count) {
39      int remaining = end - start;
40      var mt = new FastRandom(seed);
41      for (int i = start; i < end && count > 0; i++) {
42        double probability = mt.NextDouble();
43        if (probability < ((double)count) / remaining) {
44          count--;
45          yield return i;
46        }
47        remaining--;
48      }
49    }
50  }
51}
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