重边怎么处理? 附上25pts代码(加上RE的点50pts)

#include<bits/stdc++.h>
using namespace std;
int n,m,ut,vt,wt,dfn[1000010],low[1000010],cnt,cntbcc;
vector<int> g[1000010];
vector<int> bcc[1000010];
stack<int> s;
void tarjan(int u,int fa) {
	dfn[u] = low[u] = ++cnt;
	s.push(u);
	for (int i = 0;i < g[u].size();i ++) {
		int v = g[u][i];
		if (!dfn[v]) {
			tarjan(v,u);
			low[u] = min(low[u],low[v]);
			//if (low[v] > dfn[u]) bridge.push_back(make_pair(u,v));//
		} else if (v != fa) low[u] = min(low[u],dfn[v]);
	}
	if (low[u] == dfn[u]) {
		++ cntbcc;
		while (s.top() != u) {
			bcc[cntbcc].push_back(s.top());
			s.pop();
		}
		bcc[cntbcc].push_back(s.top());
		s.pop();
	}
	return;
}
int main() {
	scanf("%d%d",&n,&m);
	for (int i = 1;i <= m;i ++) {
		scanf("%d%d",&ut,&vt);
		g[ut].push_back(vt);
		g[vt].push_back(ut);
	}
	for (int i = 1;i <= n;i ++)
		if (!dfn[i]) tarjan(i,0);
	printf("%d\n",cntbcc);
	for (int i = 1;i <= cntbcc;i ++) {
		printf("%d ",bcc[i].size());
		for (int j = 0;j < bcc[i].size();j ++)
			printf("%d ",bcc[i][j]);
		printf("\n");
	}
	return 0;
}