public static List<int> ScoreFrames(List<int> rolls)
    {
        List<int> frames = new List<int>();

        for (int i = 1; i < rolls.Count && frames.Count < 10; i += 2) {

            if (rolls[i - 1] + rolls[i] < 10) {                         // Normal OPEN frame
                frames.Add(rolls[i - 1] + rolls[i]);
            } else if (rolls.Count - i > 1) {                           // STRIKE or SPARE look ahead
                frames.Add(rolls[i - 1] + rolls[i] + rolls[i + 1]);
                i -= rolls[i - 1] / 10;                                 // Set iterator one step back on STRIKE
            }
        }
        return frames;
    }