题目描述 Brain Network (hard) 这个问题就是给出一个不断加边的树,保证每一次加边之后都只有一个连通块(每一次连的点都是之前出现过的),问每一次加边之后树的直径. 算法 每一次增加一条边之后,树的直径长度要么不变,要么会增加1,并且如果树的直径长度增加1了,新的直径的端点其中一个必然是新增的点,而另一个是原来直径的某个端点.关于为什么可以这样做,在Quora上有个回答解释地不错,可以参考. 实现 所以这个问题其实就是要计算树上任意两个点的距离,LCA可以很轻松地处理. 可以一次…

Description One particularly well-known fact about zombies is that they move and think terribly slowly. While we still don't know why their movements are so sluggish, the problem of laggy thinking has been recently resolved. It turns out that the rea…

Description Tonight is brain dinner night and all zombies will gather together to scarf down some delicious brains. The artful Heidi plans to crash the party, incognito, disguised as one of them. Her objective is to get away with at least one brain,…

Description Further research on zombie thought processes yielded interesting results. As we know from the previous problem, the nervous system of a zombie consists of n brains and m brain connectors joining some pairs of brains together. It was obser…

G. Fake News (easy) time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output As it's the first of April, Heidi is suspecting that the news she reads today are fake, and she does not want to look sil…

Description Heidi's friend Jenny is asking Heidi to deliver an important letter to one of their common friends. Since Jenny is Irish, Heidi thinks that this might be a prank. More precisely, she suspects that the message she is asked to deliver state…

Description Heidi has finally found the mythical Tree of Life – a legendary combinatorial structure which is said to contain a prophecy crucially needed to defeat the undead armies. On the surface, the Tree of Life is just a regular undirected tree w…

Description The zombies are gathering in their secret lair! Heidi will strike hard to destroy them once and for all. But there is a little problem... Before she can strike, she needs to know where the lair is. And the intel she has is not very good.…

Description "The zombies are lurking outside. Waiting. Moaning. And when they come..." "When they come?" "I hope the Wall is high enough." Zombie attacks have hit the Wall, our line of defense in the North. Its protection is…

Description The marmots have prepared a very easy problem for this year's HC2 – this one. It involves numbers n, k and a sequence of n positive integersa1, a2, ..., an. They also came up with a beautiful and riveting story for the problem statement.…