数据过水

#include <algorithm>
#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

const int N = 1e4 + 5;

vector<int> g[N];
int n, m, tot, cnt;
int dfn[N], low[N];
pair<int, int> e[N];

void dfs(int u, int fa)
{
    dfn[u] = low[u] = ++tot;
    for (auto v : g[u])
    {
        if (!dfn[v])
        {
            dfs(v, u);
            low[u] = min(low[u], low[v]);
            if (low[v] > dfn[u]) e[++cnt] = {min(u, v), max(u, v)};
        }

        if (v != fa) low[u] = min(low[u], dfn[v]);
    }
}

int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 1, u, v; i <= m; i++)
    {
        scanf("%d%d", &u, &v);
        g[u].push_back(v), g[v].push_back(u);
    }

    for (int i = 1; i <= n; i++)
        if (!dfn[i]) dfs(i, i);

    sort(e + 1, e + cnt + 1);

    for (int i = 1; i <= cnt; i++)
        printf("%d %d\n", e[i].first, e[i].second);
        
    return 0;
}