需要索引（如算距离、下标）：栈存索引，用 nums[stack.at(-1)] 取值比较。
Point lookups are useful, but the operation you'll reach for more often is a range query: give the tree a rectangular region and retrieve every point inside it, without scanning the entire dataset.
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Gotta watch it all.
The weight of each term is given by the proportion of each sub-triangle area with respect to the total triangle area . Algebraically, this can be expressed like so:
В Финляндии предупредили об опасном шаге ЕС против России09:28