使用C#.NET列举组合数前N项和

列举如下列所示的组合数前N项和，代码如下(递归方法里注意去重)：

    static void Main(string[] args)
    {
        List<string> list = GetSumOfPermutation("abcde", 5).ToList();
        File.AppendAllLines(@"C:Sample.txt", list,Encoding.UTF8);
    }

    static IEnumerable<string> GetSumOfPermutation(string source, int maxCount)
    {
        string temp = string.Empty;
        if (maxCount > 0)
        {
            maxCount = maxCount - 1;
            for (int i = 0; i < source.Length; i++)
            {
                foreach (var cur in GetSumOfPermutation(source, maxCount))
                {
                    if (cur.Contains(source[i]))
                        continue;
                    temp = source[i] + cur;
                    //Console.WriteLine(temp);
                    yield return temp;
                }
                temp = source[i].ToString();
                //Console.WriteLine(temp);
                yield return temp;
            }
        }
    }