Connect cities

input/code.cpp: In function 'std::vector<int> dfs(std::vector<std::vector<int> >&, std::vector<int>&)':
input/code.cpp:24:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for (int i = 0; i < adj.size(); i++) {
      |                     ~~^~~~~~~~~~~~
input/code.cpp: In function 'int main()':
input/code.cpp:58:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   58 |     for (int i = 0; i < disconnected_leads.size() - 1; ++i)
      |                     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

//Driver Code Starts
#include <iostream>
#include <vector>

using namespace std;

void dfsRec(vector<vector<int>> &adj, 
vector<bool> &visited, int s, vector<int> &res) {
    
    visited[s] = true;

    res.push_back(s);

    for (int i : adj[s])
        if (visited[i] == false)
            dfsRec(adj, visited, i, res);
}

vector<int> dfs(vector<vector<int>> &adj, vector<int> &disconnected_leads) {
    vector<bool> visited(adj.size(), false);
    vector<int> res;
    // Loop through all vertices 
    // to handle disconnected graph
    for (int i = 0; i < adj.size(); i++) {
        if (visited[i] == false) {
            disconnected_leads.push_back(i + 1);
            dfsRec(adj, visited, i, res);
        }
    }

    return res;
}


void addEdge(vector<vector<int>>& adj, int u, int v) {
    adj[u].push_back(v);
    adj[v].push_back(u);
}

int main() {
    int n_cities, n_roads;

    cin >> n_cities >> n_roads;

    vector<vector<int>> adj(n_cities);
    
    int city1, city2;
    for(int i = 0; i < n_roads; ++i)
    {
        cin >> city1 >> city2;
        addEdge(adj, city1 - 1, city2 - 1);
    }

    vector<int> disconnected_leads;
 
    vector<int> res = dfs(adj, disconnected_leads); 
    cout << disconnected_leads.size() - 1 << "\n";
    for (int i = 0; i < disconnected_leads.size() - 1; ++i)
        cout << disconnected_leads[i] << " " << disconnected_leads[i + 1] << "\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