models, their efforts were still influential enough that later ATMs inherited
思路：倒序单调栈。弹出所有 ≤ 当前身高的元素（这些人都能被看到），count 为弹出数量；若栈非空，还能看到栈顶（第一个更高的人），故 +1。能看到的人数 = count + (栈非空 ? 1 : 0)。
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Every point gets examined, regardless of where it sits. Points on the opposite side of the map get the same treatment as points right next to the query region. We're doing a lot of unnecessary work.