发现从顶点入手不太方便,我们从这个“公共部分最长”开始考虑问题,因为要求这一条公共部分的链最长,可以联想到树的直径,那么本题就是要求一条类似于直径的东西使两个端点除了直径这一条链之外还有不少于两个的儿子,我们只要把这两个儿子交叉输出一下就得到了本题的答案.只要两次$dfs$就可以分别求出这一条链的两个端点了,$dfs$的时候维护一下最大和次大两个儿子更新答案即可.时间复杂度$O(n)$.Code: #include <cstdio> #include <cstring> #incl…

Description You are given an undirected unweighted tree consisting of \(n\) vertices. An undirected tree is a connected undirected graph with \(n−1\) edges. Your task is to choose two pairs of vertices of this tree (all the chosen vertices should be…

由于换了台电脑,而我的贪心 & 构造能力依然很拉跨,所以决定再开一个坑( 前传: 贪心/构造/DP 杂题选做 u1s1 我预感还有Ⅲ(欸,这不是我在多项式Ⅱ中说过的原话吗) 24. P5912 [POI2004]JAS 一开始直接莽了个点分治,当我测过了样例美滋滋地一交,发现自己获得了 20 分的好成绩之后,才发现事情有那么亿点点不对劲( 不难发现,题目等价于求高度最小的点分树的高度,直接求有点困难,我们不妨来对其进行一些转化:我们考虑给每个点一个标号,那么问题可以转化为,求使得任意两个标号相同…

写之前,先发表下感慨:好久没写题解了,也许是因为自己越来越急利了,也可以说是因为越来越懒了. A. Diverse Substring 直接找一找有没有相邻的两个不同的字符即可. B. Vasya and Books 分别记录书本摆放顺序$a[]$,取书顺序$b[]$,每本书的位置$pos[]$,每本书在不在书堆上$in[]$,书堆最顶端的书的位置$top$(因为用的是数组,元素位置是固定的). 然后,按照题意枚举输入的取书顺序$b[]$,同时记录答案$ans$,更新$top$即可. C. Va…

E. Wizards and Bets 题目连接: http://www.codeforces.com/contest/167/problem/E Description In some country live wizards. They like to make weird bets. Two wizards draw an acyclic directed graph with n vertices and m edges (the graph's vertices are numbere…

P2959 [USACO09OCT]悠闲漫步The Leisurely Stroll 题目描述 Bessie looks out the barn door at the beautiful spring day and thinks to herself, 'I'd really like to enjoy my walk out to the pastures for the tender spring grass.' She knows that once she leaves the b…

  Choosing a Rendering Path 选择渲染路径 Unity supports a number of rendering techniques, or ‘paths’. An important early decision which needs to be made when starting a project is which path to use. Unity’s default is 'Forward Rendering”. Unity支持许多渲染技术或“路径…

Given a binary tree, return all root-to-leaf paths. For example, given the following binary tree: 1 / \ 2 3 \ 5 All root-to-leaf paths are: ["1->2->5", "1->3"] 这道题给我们一个二叉树,让我们返回所有根到叶节点的路径,跟之前那道Path Sum II 二叉树路径之和之二很类似,比那道稍微简单一…

Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively in the grid. For example, There is one obstacle in the middl…

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in t…