（二）采取预收款方式提供建筑服务；
* 核心思路：找初始无序边界 + 计算区间最值 + 扩展边界
，更多细节参见Line官方版本下载
let imports = {。Line官方版本下载对此有专业解读
Imagine a vast shopping mall parking lot with thousands of individual parking spots and internal lanes (representing road segments within a cluster). No matter how complex it is inside, there are usually only a few key exits to the main roads. Our goal was to identify these natural "exits" for each map cluster. For instance, the complex road network around Amsterdam Airport Schiphol (see on OpenStreetMap) has many internal roads but limited primary access points.