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", ).ToList();
         File.AppendAllLines(@"C:\Sample.txt", list,Encoding.UTF8);
     }

     static IEnumerable<string> GetSumOfPermutation(string source, int maxCount)
     {
         string temp = string.Empty;
         if (maxCount > )
         {
             maxCount = maxCount - ;
             for (int i = ; 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;
             }
         }
     }