pku 3041 Asteroids（最小点覆盖）

int n,k;
vector<int> graph[505];
bool bmask[505];
int cx[505],cy[505];

int findPath(int u){
    int L=graph[u].size();
    rep(i,0,L-1){
        int v=graph[u][i];
        if(!bmask[v]){
            bmask[v]=true;
            if(cy[v]==-1||findPath(cy[v])){
                cy[v]=u;
                cx[u]=v;
                return 1;
            }
        }
    }
    return 0;
}
int MaxMatch(){
    int ans=0;
    rep(i,1,n) cx[i]=cy[i]=-1;
    rep(i,1,n) if(cx[i]==-1){
        mem(bmask,false);
        ans+=findPath(i);
    }
    return ans;
}

int main(){
    while(scanf("%d%d",&n,&k)!=EOF){
        rep(i,1,n) graph[i].clear();
        while(k--){
            int r,c;
            scanf("%d%d",&r,&c);
            graph[r].push_back(c);
        }
        int dd=MaxMatch();
        printf("%d\n",dd);
    }
}