题目链接 题意:有向图中有n(1 <= n <= 200)个点,无自环或者环的节点个数至少为3.给定每条边的最小流量和最大流量,问每条边的可行流量为多少? 思路:一般求解的网络流并不考虑下界问题,即流量可以为0,在有下界时,我们只需将上界变成r-l,这时还需要满足流量守恒,增加源点s和汇点t,当点u的流入大于流出时,将点u与s连边,容量即为多出的流量.同理当u流出大于流入时,多出来的流出的流量连到汇点t;直接跑最大流:这时得到的只是网络中的可行流: 为什么处理完下界之后是这样与超级源点和汇点连…

题意:无源无汇有上下界的可行流 模型 思路:首先将所有边的容量设为上界减去下界,然后对一个点i,设i的所有入边的下界和为to[i],所有出边的下界和为from[i],令它们的差为dif[i]=to[i]-from[i],根据流量平衡原理,让出边和入边的下界相抵消,如果dif[i]>0,说明入边把出边的下界抵消了,还剩下dif[i]的流量必须要流过来(否则不满足入边的下界条件),这时从源点向i连一条容量为dif[i]的边来表示即可,如果dif[i]<0,同理应该从i向汇点连一条容量为-dif[i…

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…

[题目链接] http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=20757 [题意] 求有容量上下界的无源无汇可行流. [思路] 无源无汇可行流要求所有的顶点都满足流量平衡. 基本思路是转化成最大流来做. 对于边(u,v,b,c),连边(u,v,c-b).为了保持流量平衡,我们还需要连边         1.(S,u,inB[u]-outB[u])  inB>outB 2.(u,T,outB[u]-inB[u])  outB>…

时间限制:0.5s 空间限制:6M 题意: 显然就是求一个无源汇有上下界的网络流的可行流的问题 Solution: 没什么好说的,直接判定可行流,输出就好了 code /* 无汇源有上下界的网络流 */ #include <iostream> #include <cstring> #define ms(a,b) memset(a,b,sizeof a) using namespace std; ; struct node { int u, v, c, ne; } edge[MAXN…

题意: 给定n个点和m条边, 每条边有流量上下限[b,c], 求是否存在一种流动方法使得每条边流量在范围内, 而且每个点的流入 = 流出 分析: 无源汇有上下界最大流模板, 记录每个点流的 in 和 out , 然后如果一个点 i 的in > out,  从源点i连一条边到in, out > in 就从i 连一条边到 v. #include <cstdio> #include <iostream> #include <cstring> #include &l…

http://acm.sgu.ru/problem.php?contest=0&problem=194 题意:m条有向边,有上下界,求最大流. 思路:原图中有u-v low[i],high[i] 建图就是u->v,high[i]-low[i],同时du[u]-=low[i],du[v]+=low[i],然后对于每个点i,如果du[i]>0,那就S->i,du[i],若是du[i]<0那就i->T ,-du[i],然后判断S出去的流是不是满流,不是就无解,否则每条边流量…

Description The terrorist group leaded by a well known international terrorist Ben Bladen is buliding a nuclear reactor to produce plutonium for the nuclear bomb they are planning to create. Being the wicked computer genius of this group, you are res…

题目链接: http://acm.sgu.ru/problem.php?contest=0&problem=194 题目大意: n个点(n<20000!!!不是200!!!RE了无数次),m条边(管子)(m范围好像没说,我开了10^6),每个点流入的和流出的液体要相等,每条边(管子)有上下界流量,问是否有解,有解YES无解NO,有解还要输出每条边的流量. 题目输入样例略坑,我以为要多组数据输入输出TEST #1 什么的.后来仔细看了Input发现只有一组吧应该,保险起见还是写了多组,但是不用…

Reactor Cooling time limit per test: 0.5 sec. memory limit per test: 65536 KB input: standard output: standard The terrorist group leaded by a well known international terrorist Ben Bladen is buliding a nuclear reactor to produce plutonium for the nu…