source: branches/PushGP/HeuristicLab.PushGP/HeuristicLab.Problems.ProgramSynthesis/Push/Extensions/CollectionExtensions.cs @ 15287

using System.Collections.Generic;

namespace HeuristicLab.Problems.ProgramSynthesis.Push.Extensions {
  using HeuristicLab.Core;
  using HeuristicLab.Random;

  public static class CollectionExtensions {
    public static T Random<T>(this IReadOnlyList<T> source, IRandom random = null) {
      random = random ?? new MersenneTwister();
      var x = random.Next(source.Count);

      return source[x];
    }

    public static int HashCode<T>(this IReadOnlyList<T> source) {
      var hash = 19 * 31 + typeof(T).FullName.GetHashCode();

      for (var i = 0; i < source.Count; i++)
        hash = hash * 31 + source[i].GetHashCode();

      return hash;
    }

    public static int HashCode<T>(this IEnumerable<T> source) {
      var hash = 19 * 31 + typeof(T).FullName.GetHashCode();

      foreach (var item in source)
        hash = hash * 31 + item.GetHashCode();

      return hash;
    }
  }
}