/// <inheritdoc cref="GetEnumerator"/>
public IEnumerator <int[]> iterator()
{
if (k == 0 ||
k == n)
{
return(new SingletonIterator(MathArrays.natural(k)));
}
switch (iterationOrder)
{
case IterationOrder.LEXICOGRAPHIC:
return(new LexicographicIterator(n, k));
default:
throw new MathInternalError(); // Should never happen.
}
}
/// <inheritdoc/>
/// <remarks>
/// This method calls <see cref="MathArrays.shuffle(int[],RandomGenerator)"/>
/// in order to create a random shuffle of the set
/// of natural numbers <c>{ 0, 1, ..., n - 1 </c>}.
/// </remarks>
/// <exception cref="NumberIsTooLargeException"> if <c>k > n</c>.</exception>
/// <exception cref="NotStrictlyPositiveException"> if <c>k <= 0</c>.</exception>
public int[] nextPermutation(int n, int k)
{
if (k > n)
{
throw new NumberIsTooLargeException <Int32, Int32>(new LocalizedFormats("PERMUTATION_EXCEEDS_N"), k, n, true);
}
if (k <= 0)
{
throw new NotStrictlyPositiveException <Int32>(new LocalizedFormats("PERMUTATION_SIZE"), k);
}
int[] index = MathArrays.natural(n);
MathArrays.shuffle(index, getRandomGenerator());
// Return a new array containing the first "k" entries of "index".
return(MathArrays.copyOf(index, k));
}