The spatial view (the grid of rectangles) and the tree view (the hierarchy of nodes) represent the same structure. Searching for a point means walking down the tree: at each node, you check which of the four children contains your target coordinate and recurse into that child. You never visit the other three.
这些看起来是搬箱子，背后其实是一整套复杂的任务规划与执行。
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She added: "If you are collecting your food in a caddy, you really get to see firsthand what you're throwing away. I think that can really prompt some rethinking."
另一件让我很欣慰的是，我家孩子的免疫力还可以，一个冬天除了经常咳嗽，没出现大问题，相比他们班的其他孩子来说，简直是超人体质。