50分substack#3 4 MLE求助

#include <math.h>
#include <string.h>
#include <algorithm>
#include <stack>
#include <vector>
#define ll long long
#define INF 10000001
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;
const int N=11000000;
int n,m; 
vector<int> g[N];
stack<int> stk;
int bri[N],d[N];
int dfn[N],low[N],tot;
int cnt;
int dcc[N];
vector<int> a[N];
struct {
    int to,nxt;
}e[N];
int head[N],ct=1;
void add(int u,int v){
    e[++ct].to=v;
    e[ct].nxt=head[u];
    head[u]=ct;
}
void tarjan(int x,int edg){
    dfn[x]=low[x]=++tot;
    stk.push(x);
    for(int i=head[x];i;i=e[i].nxt){
        int v=e[i].to;
        if(!dfn[v]){
            tarjan(v,i);
            low[x]=min(low[x],low[v]);
            if(low[v]>dfn[x]){
                bri[i]=bri[i^1]=1;
            }
        }else if(i!=(edg^1)){
            low[x]=min(low[x],dfn[v]);
        }
    }
    if(dfn[x]==low[x]){
        ++cnt;
        while(1){
            int y=stk.top();
            stk.pop();
            dcc[y]=cnt;
            a[cnt].push_back(y);
            if(x==y) break;
        }
    }
}
int main(int argc, char** argv) {
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        int a,b;
        cin>>a>>b;
        add(a,b);
        add(b,a);
    }
    for(int i=1;i<=n;i++){
        if(!dfn[i]){
            tarjan(i,0);
        }
    }
    cout<<cnt<<endl;
    for(int i=1;i<=cnt;i++){
    cout<<a[i].size()<<" ";
        for(int v:a[i]){
            cout<<v<<" ";
        }
        cout<<endl;
    }
    return 0;
}