tarjan求强连通

#include <bits/stdc++.h>
using namespace std;
#define _ 0
const int maxn = 2e5+5;
vector<int>E[maxn];
int dfn[maxn],low[maxn],tot,n,m,vis[maxn],ans=maxn;
stack<int>s;
void tarjan(int x){
    low[x]=dfn[x]=++tot;
    s.push(x);vis[x]=1;
    for(int i=0;i<E[x].size();i++){
        int v=E[x][i];
        if(!dfn[v]){
            tarjan(v);
            low[x]=min(low[x],low[v]);
        }
        else if(vis[v]){
            low[x]=min(low[x],dfn[v]);
        }
    }
    if(low[x]==dfn[x]){
        int sz = 0;
        while(1){
            int now = s.top();
            s.pop(); vis[now]=0;
            sz++;
            if(now == x) break;
        }
        if(x==1)printf("%d\n",sz);
    }
}
int main(){
    scanf("%d%d", &n, &m);
    for(int i=1; i<=m; i++){
        int u,v;
        scanf("%d%d",&u,&v);
        E[u].push_back(v);
    }
    tarjan(1);
    return (0^_^0);
}