Hearthstone: ハースストーンのスプリットダメージの期待値プログラム省メモリ化

ふと、前回書いたプログラム
simplestar-tech.hatenablog.com

について
デバッグ用に組み合わせ一覧を記録していましたが
ほしいのはカードごとの撃破率なので、計算結果が出たら
加算していけば答えを変えずに省メモリ化できることに気づきまして
下記の通り、省メモリ化を施しました。
若干の高速化もできています。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

class SplitDamageCalculator
{
    public void CalculateP(int[] cardLives, int damageCount, out float[] cardDefeatRates)
    {
        int numCards = cardLives.Length;
        cardDefeatRates = new float[numCards];
        float probability = 1;
        int totalLife = 0;
        for (int j = 0; j < numCards; j++)
            totalLife += cardLives[j];
        if (damageCount >= totalLife)
        {
            for (int i = 0; i < numCards; i++)
                cardDefeatRates[i] = 1;
        }
        else if (0 < damageCount)
        {
            _ListCombinationProbability(ref cardDefeatRates, ref cardLives, probability, numCards, damageCount - 1);
        }
        else
        {
            for (int i = 0; i < numCards; i++)
                cardDefeatRates[i] = 0;
        }
    }

    private static void _ListCombinationProbability(ref float[] cardDefeatRates, ref int[] rootCombination, float rootProbability, int numCards, int damageCount)
    {
        if (0 > damageCount)
        {
            for (int k = 0; k < numCards; k++)
                if (0 == rootCombination[k])
                    cardDefeatRates[k] += rootProbability;
            return;
        }
        for (int i = 0; i < numCards; i++)
        {
            if (0 != rootCombination[i])
            {
                int numActiveCards = 0;
                for (int j = 0; j < numCards; j++)
                    if (0 != rootCombination[j])
                        ++numActiveCards;
                float probability = rootProbability * 1 / (float)numActiveCards;
                rootCombination[i]--;
                _ListCombinationProbability(ref cardDefeatRates, ref rootCombination, probability, numCards, damageCount - 1);
                rootCombination[i]++;
            }
        }
    }
}