学步园

题意：每头牛有想吃的食物和饮料，每头牛最多只能吃一种食物和一种饮料，给出牛的个数，食物和饮料的种类数，每头牛想要的食物和饮料的种类。

刚开始想着把牛放中间，从汇点到食物，食物到牛，牛到饮料，饮料到汇点建图，当时没想清楚就敲了，结果wrong了，后来一想这样建图的话，经过没头牛的流量就不是1了，果断拆点，把每头牛拆成两个点，流量为1

#include<stdio.h>
#include<string.h>
#define N 500
#define inf 0x3fffffff
int dis[N],gap[N],head[N],num,start,end,ans;
struct edge
{
	int st,ed,flow,next;
}E[N*10];
void addedge(int x,int y,int w)
{
	E[num].st=x;E[num].ed=y;E[num].flow=w;E[num].next=head[x];head[x]=num++;
	E[num].st=y;E[num].ed=x;E[num].flow=0;E[num].next=head[y];head[y]=num++;
}
int dfs(int u,int minflow)
{
	if(u==end)return minflow;
	int i,v,f,min_dis=ans-1,flow=0;
	for(i=head[u];i!=-1;i=E[i].next)
	{
		if(E[i].flow>0)
		{
			v=E[i].ed;
			if(dis[v]+1==dis[u])
			{
				f=dfs(v,E[i].flow>minflow-flow?minflow-flow:E[i].flow);
				E[i].flow-=f;
				E[i^1].flow+=f;
				flow+=f;
				if(flow==minflow)break;
				if(dis[start]>=ans)return flow;
			}
			min_dis=min_dis>dis[v]?dis[v]:min_dis;
		}
	}
	if(flow==0)
	{
		if(--gap[dis[u]]==0)
			dis[start]=ans;
		dis[u]=min_dis+1;
		gap[dis[u]]++;
	}
	return flow;
}
int isap()
{
	int maxflow=0;
	memset(dis,0,sizeof(dis));
	memset(gap,0,sizeof(gap));
	gap[0]=ans;
	while(dis[start]<ans)
		maxflow+=dfs(start,inf);
	return maxflow;
}
int main()
{
	int i,j,n,m,k,x,y;
	while(scanf("%d%d%d",&n,&m,&k)!=-1)
	{
		memset(head,-1,sizeof(head));
		num=0;start=0;end=2*n+m+k+1;
		for(i=1;i<=n;i++)
		{
			addedge(i,i+n,1);//拆点
			scanf("%d%d",&x,&y);
			while(x--)
			{
				scanf("%d",&j);
				addedge(2*n+j,i,1);
			}
			while(y--)
			{
				scanf("%d",&j);
				addedge(i+n,2*n+m+j,1);
			}
		}
		ans=end+1;
		for(i=1;i<=m;i++)
			addedge(start,2*n+i,1);
		for(i=1;i<=k;i++)
			addedge(2*n+m+i,end,1);
		printf("%d\n",isap());
	}
	return 0;
}