Linq的组合发电机

为了它的价值，尝试这样的事情：

public static IEnumerable<string> GetPermutations(string s){    if (s.Length > 1)        return from ch in s    from permutation in GetPermutations(s.Remove(s.IndexOf(ch), 1))    select string.Format("{0}{1}", ch, permutation);    else        return new string[] { s };}