Asteroids

#include<cstring>

#include<algorithm>

#include<cmath>

using namespace std;

const int MAXV = 505;

int pnt[MAXV*MAXV],nxt[MAXV*MAXV],head[MAXV]; //边数为500*500！！！！！

int match[MAXV];

bool vis[MAXV];

int E = 0;

void add(int u,int v){

nxt[E]=head[u];

pnt[E]=v;

head[u]=E++;

}

bool dfs(int u)

{

for(int i=head[u];i!=-1;i=nxt[i]){

int v=pnt[i];

if(!vis[v]){

vis[v]=1;

if(match[v]==-1||dfs(match[v])){

match[v]=u;

return true;

}

}

}

return false;

}

int solve(int n)

{

int ans=0;

memset(match,-1,sizeof(match));

for(int i=1;i<=n;i++)

{

memset(vis,0,sizeof(vis));

if(dfs(i)) ans++;

}

return ans;

}

int main()

{

int n,k;

memset(head,-1,sizeof(head));

memset(vis,0,sizeof(vis));

scanf("%d%d",&n,&k);

while(k--)

{

int x,y;

scanf("%d%d",&x,&y);

add(x,y);

}

printf("%d\n",solve(n));