【模板】二分图

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>
typedef long long ll;
using namespace std;
const int maxn=1e3+5,INF=0x3f3f3f3f;
ll n,m,girls[maxn],vis[maxn],ans;
vector<ll> g[maxn];
inline ll read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')w=-1;ch=getchar();
	}
	while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=getchar();
	return s*w;
}
bool Find(ll u){
	for(int i=0;i<g[u].size();i++){
		ll v=g[u][i];
		if(!vis[v]){
			vis[v]=1;
			if(girls[v]==0||Find(girls[v])){
				girls[v]=u;
				return 1;
			}
		}
	}
	return 0;
}
int main(){
	//freopen("a.in","r",stdin);
	for(int i=0;i<maxn;i++){
		g[i].clear();
	}
	n=read(),m=read();
	for(int i=1;i<=m;i++){
		ll u=read(),v=read();
		g[u].push_back(v);
	}
	for(int i=1;i<=n;i++){
		memset(vis,0,sizeof(vis));
		if(Find(i))ans++;
	}
	cout<<ans;
}

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