dfs на плюсаъ

#include<iostream>
#include<vector>
#include<string>
#include<set>
#include<algorithm>

#define ll long long
#define ld long double
#define pb push_back

using namespace std;

vector<vector<int>> g;
vector<bool> used;
vector<pair<int, int>> answ;

void dfs(int h) {
    used[h] = true;
    for (auto e : g[h]) {
        if (!used[e]) {
            answ.push_back({h, e});
            dfs(e);
        }
    }
}

int main() {
    int n, m;
    cin>>n>>m;
    g.resize(n);
    for (int i = 0; i < m; i++) {
        int x, y;
        cin>>x>>y;
        x--, y--;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    used.assign(n, false);
    dfs(0);
    for (auto e : answ) {
        cout << e.first + 1 << ' ' << e.second + 1 << '\n';
    }
    return 0;
}