解题关键:最小费用流 代码一:bellma-ford $O(FVE)$  bellman-ford求最短路,并在最短路上增广,速度较慢 #include<cstdio> #include<cstring> #include<algorithm> #include<cstdlib> #include<iostream> #include<cmath> #include<vector> #define inf 0x3f3f3f…

  Farm Tour Time Limit: 2MS   Memory Limit: 65536KB   64bit IO Format: %I64d & %I64u Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of whic…

题目链接:http://poj.org/problem?id=2135 Farm Tour Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 17672   Accepted: 6851 Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000…

Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of which contains his house and the Nth of which contains the big barn. A total M (1 <= M <…

[题意]给出一张无向图,从1开始到n,求两条没有公共边的最短路,使得路程总和最小 每条边的权值设为费用,最大流量设为1,然后就是从源点到汇点流量为2的最小费用流. 因为是规定了流量,新建一个源点和一个汇点,源点到结点1连一条最大流量为2,费用为0的边,结点N到汇点连一条最大流量为2,费用为0的边,这样就规定好流量了. #include<cstdio> #include<cstring> #include<cmath> #include<iostream> #…

两条路不能有重边,既每条边的容量是1.求流量为2的最小费用即可. //#pragma comment(linker, "/STACK:1024000000,1024000000") #include<cstdio> #include<cstring> #include<cstdlib> #include<algorithm> #include<iostream> #include<sstream> #include…

题目问的是从1到n再回到1边不重复走的最短路,本质是找1到n的两条路径不重复的尽量短的路. #include<cstdio> #include<cstring> #include<queue> #include<algorithm> using namespace std; #define INF (1<<30) #define MAXN 111 #define MAXM 2222 struct Edge{ int u,v,cap,cost,ne…

Farm Tour 题目: 约翰有N块地,家在1号,而N号是个仓库.农场内有M条道路(双向的),道路i连接这ai号地和bi号地,长度为ci. 约翰希望依照从家里出发,经过若干地后达到仓库.然后再返回家中.假设要求往返不能经过同一条道路两次,求參观路线总长度最小值. 算法分析: 用最短路求解然后在删除第一次最短路中的边在求解一次最短路.这样是否可行?应该立即就能找到反例证明该方法不能总得到最优结果吧. 于是我们放弃把问题当作去和回的这样的想法,转而将问题当作求从1号顶点到N号顶点的两条没有公共边的…

POJ 2135 Farm Tour (网络流,最小费用最大流) Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of which contains his house and the Nth of which contains the b…

题目链接:http://poj.org/problem?id=2135 Farm Tour Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 10862   Accepted: 4024 Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000…