How to find permutation of k in a given length?

Question

How can I find the permutations of k in a given length?

For example:

The word cat has 3 letters: How can I find all the permutations of 2 in the

Answer 1

Not the most efficient, but it works:

public class permutation
{
    public static List getPermutations(int n, string word)
    {
        List tmpPermutation = new List();
        if (string.IsNullOrEmpty(word) || n <= 0)
        {
            tmpPermutation.Add("");
        }
        else
        {
            for (int i = 0; i < word.Length; i++)
            {
                string tmpWord = word.Remove(i, 1);
                foreach (var item in getPermutations(n - 1, tmpWord))
                {
                    tmpPermutation.Add(word[i] + item);
                }
            }
        }
        return tmpPermutation;
    }
}