Connect cities

#include <cstdio>
#include <iostream>
#include <utility>
#include <vector>
 
using namespace std;
 
// Depth first search
void dfs(int s, bool visited[], vector<int> adj[]) {
    if (visited[s]) {
        return;
    };
    visited[s] = true;
    for (auto u: adj[s]) {
        dfs(u, visited, adj);
    }
}
 
int main (int argc, char *argv[]) {
    int n, m;
    cin >> n >> m;
    vector<pair<int, int>> roads(m);
    for (int i = 0; i < m; i++) {
        cin >> roads[i].first >> roads[i].second;
    }
    // 0 is not included in cities
    vector<int> adj[n + 1];
    bool visited[n + 1];
    for (int i = 0; i < n + 1; i++) visited[i] = false;
 
    // Add roads to adjacent structure
    for (int j = 0; j < m; j++) {
        adj[roads[j].first].push_back(roads[j].second);
        adj[roads[j].second].push_back(roads[j].first);
    }
 
    // Iterate over all the stuff
    // 1. Execute initial dfs
    // 2. check if there are unvisited nodes
    // 3. increase the added counter and execute dfs for each unconnected component
    int added = 0;
    int k = 1;
    vector<int> added_edges;
    while (!visited[k]) {
        dfs(k, visited, adj);
 
        for (int i = k; i < n + 1; i++) {
            if (!visited[i]) {
                k = i;
                added_edges.push_back(k);
                added++;
                break;
            }
        }
    }
 
    /*for (int a = 0; a < n + 1; a++) {*/
    /*    cout << a << ": " << visited[a] << "\n";*/
    /*}*/
 
    std::cout << added << "\n";
    for (auto u: added_edges) {
        cout << u - 1 << " " << u << "\n";
    }
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED