栈（stack）是先进后出的数据结构。单调栈在入栈时通过一定规则保持栈内元素有序（单调递增或单调递减），从而把「找左侧/右侧第一个更大/更小元素」从 O(n²) 降到 O(n)。
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63-летняя Деми Мур вышла в свет с неожиданной стрижкой17:54，推荐阅读夫子获取更多信息
Madeleine Finlay sits down with science editor Ian Sample and science correspondent Nicola Davis to discuss three eye-catching stories, including the impact of a powerful psychedelic on depression, answers on the death of Russian opposition leader Alexei Navalny, and an explanation to the mystery of why humans have chins
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.