Connect cities

#include <iostream>
#include <vector>
using namespace std;

void dfs(const vector<vector<int>>& g, vector<bool>& visited, int start, vector<int>& component) {
    visited[start] = true;
    component.push_back(start);

    for (int neighbor : g[start]) {
        if (!visited[neighbor]) {
            dfs(g, visited, neighbor, component);
        }
    }
}

int main() {
    int n, m;
    cin >> n >> m;

    vector<vector<int>> g(n + 1);
    
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    
    vector<vector<int>> components;
    vector<bool> visited(n + 1, false);
    
    for (int i = 1; i <= n; ++i) {
        if (!visited[i]) {
            vector<int> component;
            dfs(g, visited, i, component);
            components.push_back(component);
        }
    }
    
    int k = components.size();
    cout << k - 1 << endl;

    for (int i = 1; i < k; ++i) {
        cout << components[i-1][0] << " " << components[i][0] << endl;
    }

    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