Swap strings to get all the combinations of a string

combinations.cs

static void SwapWords(List<string> sentence, int i, List<List<string>> results)
    {
      List<List<string>> combo = new List<List<string>>();
      if (i < sentence.Count && map.ContainsKey(sentence[i])) {
        foreach (string s in map[sentence[i]]) {
          List<string> temp = new List<string>(sentence);
          temp[i] = s;
          combo.Add(temp);
        }
        foreach (List<string> ls in combo) {
          SwapWords(new List<string>(ls), i + 1, results);
        }
      }
      else {
        //Console.WriteLine(sentence.Aggregate((s1, s2) => s1 + " " + s2));
        //results.Add(sentence.Aggregate((s1, s2) => s1 + " " + s2));
        results.Add(sentence);
      }
    }