* @param arr 待排序数组
荣耀经验能否助力“千里腾飞”？，推荐阅读爱思助手下载最新版本获取更多信息
Фото: Dok. Polres Gianyar。业内人士推荐搜狗输入法2026作为进阶阅读
Source: Computational Materials Science, Volume 267，推荐阅读51吃瓜获取更多信息
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.