思路来自 ICPCCamp /* HDU 6150 - Vertex Cover [ 构造 ] | 2017 中国大学生程序设计竞赛 - 网络选拔赛 题意: 给了你一个贪心法找最小覆盖的算法,构造一组数据,使得这个程序跑出的答案是正解的三倍以上 分析: 构造一个二分图,左边 n 个节点 将左边的点进行 n 次分块,第 i 次分 n/i 块,每块的大小为 i,对于每一块都在右边建一个新的节点和这一块所有的点相连 则右边有 nlogn个节点,且每次一定优先选右边,最后取 nlogn >= 3n */…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=6150 题意:"最小点覆盖集"是个NP完全问题 有一个近似算法是说—每次选取度数最大的点(如果有多个这样的点,则选择最后一个) 让你构造一个图,使得其近似算法求出来点数是你给定的覆盖点数的至少3倍. 解法: 可以把左边的点编号1~n,将左边的点进行n次分块,第i次分块中每块的大小为i,对于每一块的点,都在右边创建一个新节点与这些点相连. ①右边的点的度数为n,n-1,n-2,...,n/2,…

http://acm.hdu.edu.cn/showproblem.php?pid=6150 #include<iostream> #include<algorithm> #include<cstring> #include<cstdio> #include<vector> #include<stack> #include<queue> #include<cmath> #include<map> #…

最近的vj好垃圾,老崩,实名吐槽 HDU - 6150 题意:给出一个错误的求最小点覆盖的函数,需要来构造一组样例,使得那个函数跑出来的答案是正解的3倍以上. 很巧妙的构造技巧,首先想法就是弄一个二分图,让正确答案是上面的n个点,我们需要构造的就是下面的点,这就不知道为什么要这样构造了.也就是分块的思想. 从1~n每次分n/i个块,每个块的大小为i,对于每个块下面就构造出一个点跟块里所有点相连. 这样下面的点就是n+n/2+n/3+n/4+...大约就是nlnn个点,那我们要求nlnn>=3n,…

A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. Now given a graph with several vertex sets, you are supposed to tell if each of them is a vertex cover or not.Input Specifi…

这里将讲解一下npc问题中set cover和vertex cover分别是什么. set cover: 问题定义: 实例:现在有一个集合A,其中包含了m个元素(注意,集合是无序的,并且包含的元素也是不相同的),现在n个集合,分别为B1.B2.....Bn.并且这n个集合的并集恰好等于A集合,即:B1UB2UB3U...UBn=A. 问题:是否存在B集合的最小子集,且他们的并集也等于A集合? 例子:集合A={1,2,3,4,5},集合B={{1,2,3},{2,4},{3,4},{4,5}}.可…

2038. Minimum Vertex Cover Time limit: 1.0 secondMemory limit: 64 MB A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. A minimum vertex cover is a vertex cover with minimal…

1134. Vertex Cover (25) 时间限制 600 ms 内存限制 65536 kB 代码长度限制 16000 B 判题程序 Standard 作者 CHEN, Yue A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. Now given a graph with several…

A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. Now given a graph with several vertex sets, you are supposed to tell if each of them is a vertex cover or not. Input Specif…

A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. Now given a graph with several vertex sets, you are supposed to tell if each of them is a vertex cover or not. Input Specif…