Record char repeating times in a string

I have a string and I want to record the char repeating times. Let me use examples.

string s = "22";
                  ||
                 "12";// I wanted, the first char '2' occurred, record as 1, the second occurred ,record as 2 because of same.

string s = "2322";
                  ||||
              "1112";  

string s = "23222222";
                  ||||||||
               "11123456"; 

What I think is to use a dictionary maybe...

My partial code, please correct me if wrong.

 public Dictionary<int, int> GetCharRepeatingTimesByIndex(string input)
        {
            Dictionary<int, int> dict = new Dictionary<int, int>();
            dict[0] = 0;
            char[] c = input.ToCharArray();
            for (int i = 0; i < c.Length - 1; i++)
            {
                dict[i+1] = 0;
                if (c[i + 1] != c[i])
                {
                    dict[i + 1] = dict[i] + 1;
                }
            }
            return dict;
        }