2076.cpp

#include <bits/stdc++.h>

using namespace std;

#define print_op(...) ostream& operator<<(ostream& out, const __VA_ARGS__& u)
template<typename A, typename B> print_op(pair<A, B>) { return out << "(" << u.first << ", " << u.second << ")"; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> print_op(T_container) { out << "{"; string sep; for (const T &x : u) out << sep << x, sep = ", "; return out << "}"; }
template<typename T> void dbg_out(string s, T x) {cerr << "\033[1;35m" << s << "\033[0;32m = \033[33m" << x << "\033[0m\n";}
template<typename T, typename... Args> void dbg_out(string s, T x, Args... args) {for (int i=0, b=0; i<(int)s.size(); i++) if (s[i] == '(' || s[i] == '{') b++; else
if (s[i] == ')' || s[i] == '}') b--; else if (s[i] == ',' && b == 0) {cerr << "\033[1;35m" << s.substr(0, i) << "\033[0;32m = \033[33m" << x << "\033[31m | "; dbg_out(s.substr(s.find_first_not_of(' ', i + 1)), args...); break;}}
#ifdef LOCAL
#define dbg(...) dbg_out(#__VA_ARGS__, __VA_ARGS__)
#else
#define dbg(...)
#endif

using ll = long long;
using ld = long double;
#define ar array
#define sz(x) ((int)x.size())
#define rep(i, a, b) for (int i = (int)(a); i < (int)(b); i++) 
#define all(a) (a).begin(), (a).end()

const int MAX_N = 1e5 + 5;
const int MAX_L = 20;
const int MAX_C = 26;
const ll MOD = 1e9 + 7;
const ll INF = 1e9;
const ld EPS = 1e-9;

int n, m, dfsCounter;
int dfs_num[MAX_N], dfs_low[MAX_N], visited[MAX_N];
vector<int> adj[MAX_N];
vector<ar<int,2>> bridges;
 
void dfs(int u, int p = -1) {
    dfs_num[u] = dfs_low[u] = dfsCounter++;
    visited[u] = 1;
    int num_child = 0;
    for (int v : adj[u]) {
        if (v == p) continue; 
        // back edge
        if (visited[v]) dfs_low[u] = min(dfs_low[u], dfs_num[v]); 
        // tree edge
        else { 
            dfs(v, u);
            dfs_low[u] = min(dfs_low[u], dfs_low[v]);  
            num_child++;
            if (dfs_low[v] > dfs_num[u]) 
                bridges.push_back({u, v});
        }
    }
}

// Bridges and Articulation Points

void solve(int tc = 0) {
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int u, v; cin >> u >> v; u--; v--;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int i = 0; i < n; i++)
        if (!visited[i])
            dfs(i);
    cout << sz(bridges) << "\n";
    for (auto [u, v] : bridges) cout << u + 1 << " " << v + 1 << "\n";
}

signed main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL);
    int tc = 1;
    // cin >> tc;
    for (int t = 1; t <= tc; t++) {
        // cout << "Case #" << t << ": ";
        solve(t);
    }
}