谢天谢地，两头牛还活着，这意味着两万元本钱保住了。但它们摔得够呛，牛毛被跐溜掉了几大片。最棘手的是，老爸也不知道该怎么把它们带回来。
But YouTube remains the biggest disruptor
，更多细节参见51吃瓜
The efficiency depends on the query size relative to the data distribution. A small query in a sparse region prunes almost everything. A query that covers the whole space prunes nothing (because every node overlaps), degenerating to a brute-force scan. The quadtree gives you the most benefit when your queries are spatially local, which is exactly the common case for map applications, game physics, and spatial databases.
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if (n <= 1) return;