多次运行泛洪填充算法时，遇到堆栈溢出异常

我有一个排列在网格上的对象列表。我想删除任何没有路径返回到网格顶部的元素，无论是直接的还是通过它们的邻居。

我认为这样做的一个好方法是首先使网格上的所有内容可删除，然后使顶部行的任何内容不可删除。然后，我想做一个洪水填充从任何对象在顶部的行，使对象连接到他们不可删除。

我想不出一个方法来优化它。有更简单的方法来做我想做的事吗?

我可能是搬起石头砸了自己的脚，因为我使用了一个列表，而不是一个2d数组。它引入了很多额外的foreach循环。

    internal void DetectHangingObjects(int X)
    {
        //Set all objects to deletable
        for (int i = 0; i < planets.Count; i++)
            planets[i].deletable = true;
        //Set first row to not deletable
        for (int i = 0; i < planets.Count; i++)
        {
            Debug.WriteLine(planets[i].X + " " + X);
            if (planets[i].X == X) //X=0
            {
                planets[i].deletable = false;
                try
                {
                    DetectHangingNeighbours(planets[i]);
                }
                catch (Exception ee)
                { Debug.WriteLine(ee.Message); }
            }
        }          
    }
    internal void DetectHangingNeighbours(Planet planet)
    {
        if (planet == null || planet.deletable==true)
            return;
        planet.deletable = false;
        DetectHangingNeighbours(GetTopLeftNode2(planet));
        DetectHangingNeighbours(GetTopRightNode2(planet));
        DetectHangingNeighbours(GetLeftNode2(planet));
        DetectHangingNeighbours(GetRightNode2(planet));
        DetectHangingNeighbours(GetBottomLeftNode2(planet));
        DetectHangingNeighbours(GetBottomRightNode2(planet));
    }
    //The following methods check the six adjacent objects and returns them to the caller if they match
    internal Planet GetTopLeftNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X - planetSize && gridPlanet.Y == planet.Y - yOffset)
                return gridPlanet;
        return null;
    }
    internal Planet GetTopRightNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X - planetSize && gridPlanet.Y == planet.Y + yOffset)
                return gridPlanet;
        return null;
    }
    internal Planet GetLeftNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X && gridPlanet.Y == planet.Y - planetSize)
                return gridPlanet;
        return null;
    }
    internal Planet GetRightNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X && gridPlanet.Y == planet.Y + planetSize)
                return gridPlanet;
        return null;
    }
    internal Planet GetBottomLeftNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X + planetSize && gridPlanet.Y == planet.Y - yOffset)
                return gridPlanet;
        return null;
    }
    internal Planet GetBottomRightNode2(Planet planet)
    {
        foreach (Planet gridPlanet in planets)
            if (gridPlanet.X == planet.X + planetSize && gridPlanet.Y == planet.Y + yOffset)
                return gridPlanet;
        return null;
    }