代码

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
forward_list<int> E[N];
int vis[N];
mt19937 rg;
void dfs(int u) {
    vis[u] = 1;
    for (auto v : E[u])
        if (!vis[v]) dfs(v);
}
int main() {
    int n = 1e5;
    for (int i = 1; i <= n << 4; ++i) {
        int u = rg() % n + 1, v = rg() % n + 1;
        E[u].emplace_front(v), E[v].emplace_front(u);
    }
    dfs(1);
}

评测结果