「我們以前每個月會外出吃兩次飯，」住在伊朗第二大城市伊斯法罕（Isfahan）的瑪爾珍（Marjan） 說，「現在我們根本不能去了。我們必須把那筆錢省下來付房租。」
* @param arr 待排序数组
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The quadtree is the two-dimensional case of a broader family of space-partitioning data structures. Octrees extend the same idea to three dimensions (splitting cubes into eight children), KD-trees use alternating axis-aligned splits (splitting along x, then y, then x again), and R-trees group nearby objects into bounding rectangles. Each variant makes different tradeoffs between construction time, query speed, and update cost.
However, this flexibility came at a cost for complex routes: