regex 4

    DmgProb[] regex3(string input = "0[18/6]2[20/5]10[15/4]")
    {
        string lastIndexPattern = @"(?<index>\d+)(\[(\d+)/(\d+)\])$";
        int lastIndex = int.Parse(Regex.Match(input, lastIndexPattern).Groups["index"].Value);
        string pattern = @"(?<index>\d+)\[(?<damage>\d+)/(?<probability>\d+)\]";
        DmgProb[] arr = new DmgProb[lastIndex];
        List<DmgProb> matches = new List<DmgProb>();
        Dictionary<int, DmgProb> indexedDictionary = new Dictionary<int, DmgProb>();
        foreach(Match m in Regex.Matches(input, pattern))
        {
            indexedDictionary.Add(
                int.Parse(m.Groups["index"].Value),
                new DmgProb{
                    damage      = float.Parse(m.Groups["damage"]     .Value),
                    probability = float.Parse(m.Groups["probability"].Value)
                }
                );
        }
        DmgProb lastDmgProb = indexedDictionary[0];
        for(int i = 0; i < lastIndex; i++)
        {
            if(!indexedDictionary.ContainsKey(i))
                arr[i] = lastDmgProb;
            else
                arr[i] = lastDmgProb = indexedDictionary[i];
        }
        return arr;
    }