mcfx's blog - Codeforces 809E. Surprise me! 的评论 /archives/236/ zh-CN ###Description 给一棵树，每个点点权 $$a_i$$，保证 $$a_i$$各不相同，现在随机选两个点 $$u,v$$，求 $$f(u,v)=\phi(a_u\cdot a_v)\c... Thu, 08 Jun 2017 13:03:13 +0800 Thu, 08 Jun 2017 13:03:13 +0800 Sengxian /archives/236/#comment-11 /archives/236/#comment-11 Thu, 08 Jun 2017 13:03:13 +0800 Sengxian 似乎虚树可以做到一个 log，感觉挺妙的。

https://blog.sengxian.com/solutions/cf-809e

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