/// <summary>
/// Attempts to convert a text representation into a permutation.
/// </summary>
/// <param name="text">A text representation of the permutation.</param>
/// <param name="output">The corresponding permutation.</param>
/// <returns>True if the conversion succeeded, otherwise false.</returns>
/// <remarks>
/// <para>For information on supported text representations, see <see cref="Parse"/>.</para>
/// </remarks>
public static bool TryParse(string text, out Permutation output)
{
output = null;
if (text == null)
{
return(false);
}
bool success = false;
if ((text.Length > 0) && (text[0] == '['))
{
// try to parse as ordering
PermutationAsMap map;
success = PermutationAsMap.TryParse(text, out map);
if (success)
{
output = new Permutation(map);
}
}
else
{
// try to parse as cycles
PermutationAsCycles cycles;
success = PermutationAsCycles.TryParse(text, out cycles);
if (success)
{
output = new Permutation(cycles);
}
}
return(success);
}
public static bool TryParse(string text, out PermutationAsMap result)
{
result = null;
if (text.Length < 2)
{
return(false);
}
if ((text[0] != '[') || (text[text.Length - 1] != ']'))
{
return(false);
}
string[] mapText = text.Substring(1, text.Length - 2).Split((char[])null, StringSplitOptions.RemoveEmptyEntries);
int[] map = new int[mapText.Length];
bool[] flags = new bool[mapText.Length];
for (int i = 0; i < map.Length; i++)
{
int value;
if (!Int32.TryParse(mapText[i], out value))
{
return(false);
}
if ((value < 0) || (value > (map.Length - 1)))
{
return(false);
}
if (flags[value])
{
return(false);
}
map[i] = value;
flags[value] = true;
}
result = new PermutationAsMap(map);
return(true);
}
/// <summary>
/// Returns the identity permutation of the given dimension.
/// </summary>
/// <param name="dimension">The number of elements on which the permutation acts.</param>
/// <returns>The identity permutation of the requested dimension.</returns>
public static Permutation Identity(int dimension)
{
if (dimension < 0)
{
throw new ArgumentOutOfRangeException(nameof(dimension));
}
return(new Permutation(PermutationAsMap.Identity(dimension)));
}
/// <summary>
/// Get a random permutation.
/// </summary>
/// <param name="dimension">The number of elements on which the permutation acts.</param>
/// <param name="rng">A random number generator.</param>
/// <returns>A random permutation of the specified dimension. All permutations of the specified dimension are equally likely.</returns>
public static Permutation GetRandomPermutation(int dimension, Random rng)
{
if (dimension < 1)
{
throw new ArgumentOutOfRangeException(nameof(dimension));
}
if (rng == null)
{
throw new ArgumentNullException(nameof(rng));
}
return(new Permutation(PermutationAsMap.GetRandomPermutation(dimension, rng)));
}
private void ComputeMap()
{
Debug.Assert(cycles != null);
map = new PermutationAsMap(FromCyclesToMap(cycles.cycles));
}
internal Permutation(PermutationAsMap map)
{
this.map = map;
}