「小学生から大手のプログラミング教室に3年間通い、Scratchで自由自在にゲームを作れるようになりました。でも、いざ本格的なテキスト言語（PythonやJava）に進もうとした途端、まったく書けなくなって挫折してしまいました……」 ...

去年我排查过一个线上接口，QPS 不高，数据量也就几十万，但每次请求都稳定在 8 秒以上。最后定位下来的原因，说出来你可能不信——代码里用 ArrayList 去存订单号，然后在循环里反复做 contains 。把 ArrayList 换成 HashSet 之后，接口耗时从 8 秒降到了 0.3 秒。这，就是集合性能优化的典型现场。

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支持随机访问（基于索引的访问速度快，时间复杂度为 O(1)O(1)）。 插入和删除操作较慢（在中间位置插入或删除需要移动元素，时间复杂度为 O(n)O(n)）。 自动扩容（当容量不足时，底层数组会 ...

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Posts from this topic will be added to your daily email digest and your homepage feed. A new Alexa Shopping List widget for iPhone and Android makes viewing your voice-assistant generated grocery list ...