给定n个结点m条边的简单无向图，判断该图是否存在鱼形状的子图：有一个环，其中有一个结点有另外两条边，连向不在环内的两个结点。若有，输出子图的连边

题目

思路：

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define fi first
#define se second
#define lson p << 1
#define rson p << 1 | 1
const int maxn = 1e6 + 5, inf = 1e18 * 3, maxm = 4e4 + 5, mod = 1e9 + 7;
int a[maxn], b[maxn];
int n, m;
string s;
bool vis[maxn];
vector<int> G[maxn];
int from, to;
vector<int> tmp, vec;
int deg[maxn];void dfs(int u, int p){if(u == to && p == from) return;if(vis[u]) return;vis[u] = 1;tmp.pb(u);if(u == to){vec = tmp;return;}for(auto v : G[u]){dfs(v, u);}tmp.pop_back();
}
void solve(){int res =