Regions with many nearby points keep subdividing. Regions with few or no points stay large. The tree adapts to the data: dense areas get fine-grained cells, sparse areas stay coarse. The split grid is predetermined (always at midpoints), but the tree only refines cells that need it. Sparse regions stay as single large nodes while dense regions subdivide deeply.
* @param n 数组长度
，这一点在Line官方版本下载中也有详细论述
数据来源：深圳方方乐趣中英文学校
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