Visiting a Friend
Solution
Coloring a Tree
自顶向下
Hashing Trees
连续2层节点数都超过1时能异构
GCD of Polynomials
斐波那契数列为什么那么重要,所有关于数学的书几乎都会提到? - 王希的回答 - 知乎 https://www.zhihu.com/question/28062458/answer/39763094
Bipartite Segments
Weighting a Tree
Cyclic Cipher