/// <summary>
/// Rearranges all the elements in the list previously scrambled with <see cref="Scramble{TSource}(IList{TSource},int)"/> back into their original order.
/// </summary>
/// <param name="source">The input list of generic types to unscramble.</param>
/// <param name="seed">The same number used in <see cref="Scramble{TSource}(IList{TSource},int)"/> call to scramble original list.</param>
/// <typeparam name="TSource">The generic type of the list.</typeparam>
/// <remarks>This function uses the <see cref="System.Random"/> generator to perform the unscramble using a sequence that is repeatable.</remarks>
public static void Unscramble <TSource>(this IList <TSource> source, int seed)
{
if (source.IsReadOnly)
{
throw new ArgumentException("Cannot modify items in a read only list");
}
System.Random random = new System.Random(seed);
List <int> sequence = new List <int>();
int x, y, count = source.Count;
TSource currentItem;
// Generate original scramble sequence.
for (x = 0; x < count; x++)
{
// Calls random function from System namespace.
sequence.Add(random.Next(count));
}
// Unmix the data order (traverse same sequence in reverse order).
for (x = count - 1; x >= 0; x--)
{
y = sequence[x];
if (x != y)
{
// Swaps items
currentItem = source[x];
source[x] = source[y];
source[y] = currentItem;
}
}
}
/// <summary>
/// Rearranges all the elements in the list into a repeatable pseudo-random order.
/// </summary>
/// <param name="source">The input list of generic types to scramble.</param>
/// <param name="seed">A number used to calculate a starting value for the pseudo-random number sequence.</param>
/// <typeparam name="TSource">The generic type of the list.</typeparam>
/// <remarks>This function uses the <see cref="System.Random"/> generator to perform the scramble using a sequence that is repeatable.</remarks>
public static void Scramble <TSource>(this IList <TSource> source, int seed)
{
if (source.IsReadOnly)
{
throw new ArgumentException("Cannot modify items in a read only list");
}
System.Random random = new System.Random(seed);
int x, y, count = source.Count;
TSource currentItem;
// Mixes up the data in random order.
for (x = 0; x < count; x++)
{
// Calls random function from System namespace.
y = random.Next(count);
if (x != y)
{
// Swaps items
currentItem = source[x];
source[x] = source[y];
source[y] = currentItem;
}
}
}
