遞迴的核心思想就是自己呼叫自己，只要能說出來，就能用程式碼寫出來

public int 階乘(int index)
    {      

        if (index == 1)
        {
            return 1;
        }
        return index * GeiNum(index - 1);
    }

public int GeiNum(int index)
    {
        if (index == 1 || index == 2)
        {
            return 1;
        }

        return GeiNum(index - 1) + GeiNum(index - 2);

    }

    public Transform FindChildTransForm(Transform parent, string childName)
    {
        if (parent.name == childName)
            return parent;
        if (parent.childCount < 1)
            return null;
        Transform tr = null;
        for (int i = 0; i < parent.childCount; i++)
        {
            tr = FindChildTransForm(parent.GetChild(i), childName);
            if (tr != null)
                break;
        }
        return tr;
    }