Author(s): Ruixuan Dong, Xiuqin Liu
A quadtree does the same thing for two-dimensional space. It takes a rectangular region and divides it into four equal quadrants: northwest, northeast, southwest, southeast. If a quadrant has too many points in it, it subdivides again and again. Each subdivision creates smaller and smaller cells where points are densely packed.
，更多细节参见同城约会
第一百零七条 为了查明案情，人民警察可以让违反治安管理行为人、被侵害人和其他证人对与违反治安管理行为有关的场所、物品进行辨认，也可以让被侵害人、其他证人对违反治安管理行为人进行辨认，或者让违反治安管理行为人对其他违反治安管理行为人进行辨认。
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