POJ 2135 Farm Tour

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最小费用最大流.....

Description

Input

Output

Sample Input

4 5
1 2 1
2 3 1
3 4 1
1 3 2
2 4 2

Sample Output

6

Source

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

const int maxn=11000;
const int INF=(1<<30);

struct Edge
{
	int to,next,cap,flow,cost;
}edge[maxn*22];

int Adj[maxn],Size,n,m;

void init()
{
	Size=0;
	memset(Adj,-1,sizeof(Adj));
}

void addedge(int u,int v,int cap,int cost)
{
	edge[Size].to=v; 
	edge[Size].next=Adj[u];
	edge[Size].cost=cost; 
	edge[Size].cap=cap;
	edge[Size].flow=0; 
	Adj[u]=Size++;
}

void Add_Edge(int u,int v,int cap,int cost)
{
	addedge(u,v,cap,cost);
	addedge(v,u,0,-cost);
}

int dist[maxn],vis[maxn],pre[maxn];

bool spfa(int s,int t)
{
	queue<int> q;
	for(int i=0;i<n;i++)
	{
		dist[i]=INF; vis[i]=0; pre[i]=-1;
	}
	dist[s]=0; vis[s]=1; q.push(s);
	while(!q.empty())
	{
		int u=q.front();
		q.pop();
		vis[u]=0;
		for(int i=Adj[u];~i;i=edge[i].next)
		{
			int v=edge[i].to;
			if(edge[i].cap>edge[i].flow&&
					dist[v]>dist[u]+edge[i].cost)
			{
				dist[v]=dist[u]+edge[i].cost;
				pre[v]=i;
				if(!vis[v])
				{
					vis[v]=true;
					q.push(v);
				}
			}
		}
	}
	if(pre[t]==-1) return false;
	return true;
}

int MinCostMaxFlow(int s,int t,int& cost)
{
	int flow=0;
	cost=0;
	while(spfa(s,t))
	{
		int Min=INF;
		for(int i=pre[t];~i;i=pre[edge[i^1].to])
		{
			if(Min>edge[i].cap-edge[i].flow)
				Min=edge[i].cap-edge[i].flow;
		}
		for(int i=pre[t];~i;i=pre[edge[i^1].to])
		{
			edge[i].flow+=Min;
			edge[i^1].flow-=Min;
			cost+=edge[i].cost*Min;
		}
		flow+=Min;
	}
	return flow;
}

int main()
{
	while(scanf("%d%d",&n,&m)!=EOF)
	{
		init();
		for(int i=0;i<m;i++)
		{
			int u,v,c;
			scanf("%d%d%d",&u,&v,&c);
			Add_Edge(u,v,1,c);
			Add_Edge(v,u,1,c);
		}
		n++;
		Add_Edge(0,1,2,0); Add_Edge(1,0,2,0);
		Add_Edge(n-1,n,2,0); Add_Edge(n,n-1,2,0);
		int liu,cost; n++;
		liu=MinCostMaxFlow(0,n-1,cost);
		printf("%d\n",cost);
	}
	return 0;
}

POJ 2135 Farm Tour

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原文地址：http://blog.csdn.net/ck_boss/article/details/39228843