String count and replace problem

vvvv beta question
1

maybe someone has a solution for this already, its a very basic compression technique:
if you have a string like:

a---b-c--de----f-

how can i get one like this:

a3b1c2de4f1

means, replacing the occurrence count of ‘-’ with the string itself.

2

ok, now i have this method… anyone wants to optimize?

code(lang=csharp):
//replace method
List FHitList = new List();
protected string CountReplace(string s)
{
//init
FHitList.Clear();
var lastWasHit = false;
SMatch lastHit = null;

  	//gather all hits
  	for (int i=0; i<s.Length; i++)
  	{
  		if (s[i](i) == "-")
  		{
  			if(lastWasHit)
  			{
  				lastHit.count++;
  			}
  			else
  			{
  				lastHit = new SMatch();
  				lastHit.index = i;
  				lastHit.count = 1;
  			}
  			lastWasHit = true;
  		}
  		else
  		{
  			if (lastWasHit) FHitList.Add(lastHit);
  			lastWasHit = false;
  		}
  	}
  	
  	//add last hit
  	if (lastHit != null) FHitList.Add(lastHit);
  	
  	//substitude the hits
  	for (int i=FHitList.Count-1; i>=0; i--)
  	{
  		//FLogger.Log(LogType.Debug, "hit " + l[i](i).index + " " + l[i](i).count);
  		s = s.Remove(FHitList[i](i).index, FHitList[i](i).count);
  		s = s.Insert(FHitList[i](i).index, FHitList[i](i).count.ToString());
  	}
  	
  	return s;
  }

with

code(lang=csharp):
class SMatch
{
public int index;
public int count;
}

3

ok, with a scan one can build a new string on the fly:

code(lang=csharp):
//replace method
protected string CountReplace(string s, char match)
{
//init
var lastWasHit = false;
var ret = “”;
var hitCount = 0;

  	//scan the string
  	for (int i=0; i<s.Length; i++)
  	{
  		if (s[i](i) == match)
  		{
  			hitCount++;
  			lastWasHit = true;
  		}
  		else
  		{
  			if(lastWasHit) ret += hitCount.ToString();
  			hitCount = 0;
  			ret += s[i](i);
  			lastWasHit = false;
  		}
  	}
  	
  	//last hit
  	if(lastWasHit) ret += hitCount.ToString();
  	
  	return ret;
  }