[USACO4.2]完美的牛栏The Perfect Stall

#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
int n,m,level[405],iter[405];
queue<int>q;
struct edges{
	int to,cap,rev;
	edges(int t,int c,int r):to(t),cap(c),rev(r){}
};
vector<edges>G[405];
inline void addedge(int from,int to){
	G[from].push_back(edges(to,1,G[to].size()));
	G[to].push_back(edges(from,0,G[from].size()-1));
}
void bfs(int s){
	memset(level,-1,sizeof level);
	level[s]=0;
	q.push(s);
	while(!q.empty()){
		int u=q.front();q.pop();
		for(int i=0;i<G[u].size();++i){
			edges& e=G[u][i];
			if(e.cap>0&&level[e.to]<0){
				level[e.to]=level[u]+1;
				q.push(e.to);
			}
		}
	}
}
int dfs(int u,int t,int f){
	if(u==t)return f;
	for(int& i=iter[u];i<G[u].size();++i){
		edges& e=G[u][i];
		if(e.cap>0&&level[e.to]>level[u]){
			int d=dfs(e.to,t,min(f,e.cap));
			if(d){
				e.cap-=d;
				G[e.to][e.rev].cap+=d;
				return d;
			}
		}
	}
	return 0;
}
int max_flow(int s,int t){
	int flow=0;
	for(;;){
		bfs(s);
		if(level[t]<0)return flow;
		memset(iter,0,sizeof iter);
		int f;
		while(f=dfs(s,t,1))flow+=f;
	}
}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;++i){
		addedge(0,i);
		int k;
		scanf("%d",&k);
		for(;k--;){
			int x;
			scanf("%d",&x);
			addedge(i,x+n);
		}
	}
	for(int i=1;i<=m;++i)addedge(i+n,n+m+1);
	printf("%d\n",max_flow(0,n+m+1));
	return 0;
}