84pts求调

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int n,m;
vector<int> E[N];
int idx,dfn[N],vis[N],low[N],top,sta[N],scc_cnt,scc[N];
void tarjan(int u){
    low[u]=dfn[u]=++idx;
    sta[++top]=u;
    vis[u]=1;
    for (int v:E[u]){
        if (!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }else if (vis[v]) low[u]=min(low[u],dfn[v]);
    }
    if (dfn[u]==low[u]){
        ++scc_cnt;
        do{
            scc[sta[top]]=scc_cnt;
            vis[sta[top]]=0;
        }while(sta[top--]!=u);
    }
}
int main(){
    cin>>n>>m;
    for (int i=1;i<=m;++i){
        int u,v;
        cin>>u>>v;
        E[u].push_back(v);
    }
    for (int i=1;i<=n;++i){
        if (!dfn[i]) tarjan(i);
    }
    int ans=0;
    for (int i=1;i<=n;++i){
        if (scc[i]==1) ++ans;
    }
    cout<<ans;
    return 0;
}