POJ-3422-Kaka's Matrix Travels

第一次做最小费用最大流问题，参考了下网上别人的博客

地址：http://blog.youkuaiyun.com/south__wind/article/details/7932173

代码：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<queue>
using namespace std;
const int maxn=5500;
const int maxm=50100;
const int inf=1<<29;
int n,e,k,st,des,head[maxn],flow[maxm],pnt[maxm],cost[maxm],nxt[maxm],dist[maxn],pre[maxn];
bool vis[maxn];
queue<int> q;
void AddEdge(int u,int v,int f,int c)
{
    pnt[e]=v;cost[e]=c;flow[e]=f;nxt[e]=head[u];head[u]=e++;
    pnt[e]=u;cost[e]=-c;flow[e]=0;nxt[e]=head[v];head[v]=e++;
}
bool Spfa()
{
    for(int i=0;i<=des;i++)
    {
	pre[i]=-1;
	dist[i]=-1;
    }
    pre[st]=-1;
    dist[st]=0;
    q.push(st);
    while(!q.empty())
    {
	int u=q.front();
	q.pop();
	vis[u]=0;
	for(int i=head[u];i!=-1;i=nxt[i])
	{
	    if(flow[i]&&dist[pnt[i]]<dist[u]+cost[i])
	    {
		dist[pnt[i]]=dist[u]+cost[i];
		pre[pnt[i]]=i;
		if(!vis[pnt[i]])
		{
		    q.push(pnt[i]);
		    vis[pnt[i]]=1;
		}
	    }
	}
    }
    return dist[des]!=-1;
}
int maxflow()
{
    int ans=0;
    while(Spfa())
    {
	int mini=inf;	
	for(int i=pre[des];i!=-1;i=pre[pnt[i^1]])
	    mini=min(flow[i],mini);
	for(int i=pre[des];i!=-1;i=pre[pnt[i^1]])
	{
	    flow[i]-=mini;
	    flow[i^1]+=mini;
	}
	ans+=mini*dist[des];
    }
    return ans;
}
int main()
{
    while(scanf("%d%d",&n,&k)!=EOF)
    {
	e=0,st=0,des=n*n*2+1;
	memset(head,-1,sizeof(head));
	for(int i=1;i<=n;i++)
	    for(int j=1;j<=n;j++)
	    {
		int val;
		int now=(i-1)*n+j;
		scanf("%d",&val);
		AddEdge(now,now+n*n,1,val);
		if(i<n)
		{
		    AddEdge(now,now+n,inf,0);
		    AddEdge(now,now+n+n*n,inf,0);
		    AddEdge(now+n*n,now+n,inf,0);
		    AddEdge(now+n*n,now+n+n*n,inf,0);
		}
		if(j<n)
		{
		    AddEdge(now,now+1,inf,0);
		    AddEdge(now,now+n*n+1,inf,0);
		    AddEdge(now+n*n,now+1,inf,0);
		    AddEdge(now+n*n,now+n*n+1,inf,0);
		}
	    }
	AddEdge(st,1,k,0);
	AddEdge(des-1,des,k,0);
	printf("%d\n",maxflow());
    }
    return 0;
}