TextTwist_golf_csharp

void FindWords(string letters)
{
    var dictionary = new HashSet<string>(File.ReadAllLines("e"));

    for (var i = 3; i < 8; i++)
        foreach (var s in WordPermutations(letters, i).Where(dictionary.Contains).Distinct())
            Console.WriteLine(s);
}

IEnumerable<int[]> Permutations(int n, int r, int[] current = null)
{
    current = current ?? new int[] { };

    if (current.Length < r)
        for (var i = 0; i < n; i++)
            foreach (var i1 in Permutations(n, r, current.Concat(new[] { i }).ToArray()))
                yield return i1;
    else
        if (current.Length == current.Distinct().Count())
            yield return current;
}

IEnumerable<string> WordPermutations(string word, int taken)
{
    return Permutations(word.Length, taken)
        .Select(p => new string(p.Select(i => word[i]).ToArray()));
}