一种更有效的mob产卵算法

this is my method to find a free space in my world. The world consists of blocks which are collidable and non collidable. I do not want mobs to spawn in collidable blocks as they cannot move. However, this method does not work correctly, how can I improve it to make the code actually spawn all mobs in free spaces?this is my method to find a free space in my wo