Connect cities

input/code.cpp: In function 'int main()':
input/code.cpp:38:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |     for (int i = 1; i < components.size(); i++)
      |                     ~~^~~~~~~~~~~~~~~~~~~

#include <iostream>
#include <vector>

using namespace std;

void dfs(int city, vector<bool> &visited, const vector<vector<int>> &adj);

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

    vector<vector<int>> adj(n + 1);

    for (int i = 0; i < m; i++)
    {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    vector<bool> visited(n + 1, false);
    vector<int> components;

    for (int city = 1; city <= n; city++)
    {
        if (!visited[city])
        {
            components.push_back(city);
            dfs(city, visited, adj);
        }
    }

    int k = components.size() - 1;
    cout << k << endl;

    for (int i = 1; i < components.size(); i++)
    {
        cout << components[i - 1] << " " << components[i] << "\n";
    }
}

void dfs(int city, vector<bool> &visited, const vector<vector<int>> &adj)
{
    visited[city] = true;
    for (int neighbor : adj[city])
    {
        if (!visited[neighbor])
        {
            dfs(neighbor, visited, adj);
        }
    }
}

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