学步园

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
#define MAX 1001
int g[MAX][MAX],vis[MAX],link[MAX];
int n,k;
int dfs(int x){
    for(int i = 1;i <= n;i++){
        if(vis[i] == 0 && g[x][i]){
            vis[i] = 1;
            if(link[i] == -1 || dfs(link[i])){
                link[i] = x;
                return 1;
            }
        }
    }
    return 0;
}
int main(){
    while(~scanf("%d%d",&n,&k)){
            int x,y;
            memset(g,0,sizeof(g));
            memset(link,-1,sizeof(link));
            for(int i = 1;i <= k;i++){
                scanf("%d%d",&x,&y);
                g[x][y] = 1;
            }
            int ans = 0;
            for(int i = 1;i <= n;i++){
                memset(vis,0,sizeof(vis));
                if(dfs(i)) ans++;
            }
            cout<<ans<<endl;
    }
    return 0;
}