思路:无源汇有上下界可行流判定, 原来每条边转化成  下界为D  上界为 D+B   ,判断是否存在可行流即可. 为什么呢?  如果存在可行流  那么说明对于任意的 S 集合流出的肯定等于 流入的, 流出的计算的 X 肯定小于等于这个流量(X是下界之和), 计算出来的Y (上界之和)肯定大于等于 这个流量  肯定满足X<=Y. #include<cstdio> #include<cstring> #include<algorithm> #include<cm…

题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=4940 Destroy Transportation system Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others) Total Submission(s): 21    Accepted Submission(s): 17 Problem Description Tom is a…

Destroy Transportation system Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)http://acm.hdu.edu.cn/showproblem.php?pid=4940 Problem Description Tom is a commander, his task is destroying his enemy’s transportatio…

Problem Description Tom is a commander, his task is destroying his enemy’s transportation system. Let’s represent his enemy’s transportation system as a simple directed graph G with n nodes and m edges. Each node is a city and each directed edge is a…

看不懂题解以及别人说的集合最多只有一个点..... 然后试了下题解的方法http://blog.sina.com.cn/s/blog_6bddecdc0102uzka.html 首先是无源汇有上下界最大流:就是最大流基础上,无源汇,每条边的流量有上下界. 这题是给一个图,V<=200,E<=5000,每条边有destroy[i][j]和build[i][j].选一个非空点集S,令T为S的补集.若max{∑D[s][t]-D[t][s]-B[t][s]}<=0输出happy否则输出unha…

题意:有n个点和m条有向边构成的网络.每条边有两个花费: d:毁坏这条边的花费 b:重建一条双向边的花费 寻找这样两个点集,使得点集s到点集t满足 毁坏全部S到T的路径的费用和 > 毁坏全部T到S的路径的费用和 + 重建这些T到S的双向路径的费用和. 思路1: watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center&quo…

题意很容易转化到这样的问题:在一个强连通的有向图D中是否存在这样的集合划分S + T = D,从S到T集合的边权大于从T到S集合的边权. 即D(i, j)  > B(j, i) + D(j, i).或者等价地对任意集合划分:D(i, j) <= B(j, i) + D(j, i)(*). 实际上若存在可行流f,满足:D(i, j) <= f(i, j) <= B(i, j) + D(i, j),则有对于任意割满足式(*),即可以返回"happy". 关于可行流参…

Description Tom is a commander, his task is destroying his enemy’s transportation system. Let’s represent his enemy’s transportation system as a simple directed graph G with n nodes and m edges. Each node is a city and each directed edge is a directe…

职务地址:pid=4940">HDU 4940 当时这个题一看就看出来了是网络流的最小割.然后就一直在想建图. .然后突然发现,应该要让T集合的数目最少,不然仅仅要有两个,那这两个的每个都能够跑到S集合,使得T集合变小.那就仅仅能是1个了.然后. .枚举就好了. .可是尽管认为这么做肯定没错.. 可是不敢敲..由于当时都3个小时了才仅仅有10个队过了.. . 后来又想了几遍后认为这样没错,就写完交上了.果然AC. .. 代码例如以下: #include <iostream> #…

Problem Description Tom is a commander, his task is destroying his enemy’s transportation system. Let’s represent his enemy’s transportation system as a simple directed graph G with n nodes and m edges. Each node is a city and each directed edge is a…