* @param arr 待排序数组
The tree starts as a single region covering the whole space. As points arrive, they get dropped into the region that contains them. When a region exceeds its capacity (the maximum number of points it can hold before splitting), the region divides into four children, and the existing points get redistributed.。heLLoword翻译官方下载对此有专业解读
，这一点在WPS下载最新地址中也有详细论述
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understood by beginners and advanced users alike.