public class Permutation
{
List innerArray_ = new List();

public Permutation()
{
this.DigitCount = 0;
this.Permutations = 0;
this.UseRepeatation = false;
}

public bool UseRepeatation { get; set; }

public int DigitCount { get; set; }

public int Permutations { get; set; }

public List GetPermutations()
{
if (this.DigitCount > 0 && this.Permutations > 0)
GetPermutations("");

return this.innerArray_;
}

public List GetPermutations(int digitcount, int permutations)
{
this.DigitCount = digitcount;
this.Permutations = permutations;

return this.GetPermutations();
}

private void GetPermutations(string current)
{
if (current.Length < this.Permutations)
{
for (int i = 0; i < this.DigitCount; i++)
{
if (current.IndexOf(i.ToString()) < 0 || this.UseRepeatation)
GetPermutations(current + i.ToString());
}
}
else if (current.Length == this.Permutations)
this.innerArray_.Add(current);
}
}

Permutation per = new Permutation();

List result = per.GetPermutations(4, 2);

Permutation per = new Permutation();
per.UseRepeatation = true;

List result = per.GetPermutations(4, 2);