* @param arr 待排序数组
志愿者的无偿服务，对医院来说，是实实在在的“成本利器”。虽然具体财务数据未公开，但我们可以通过服务时间，大致算出它的价值：
。同城约会是该领域的重要参考
（一）有自己的名称、住所和章程；
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.