Connect cities

input/code.cpp: In function 'int main()':
input/code.cpp:39:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |     for(int i = 0; i < new_road.size(); i++){
      |                    ~~^~~~~~~~~~~~~~~~~

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void dfs(int s, vector<bool>& visited, vector<vector<int>> adj){
    if(visited[s]) return;
    visited[s] = true;
    for(auto u: adj[s]){
        dfs(u, visited, adj);
    }
}

int main(){
    int n, m, c1, c2;
    cin >> n >> m;
    vector<bool> visited(n + 1);
    vector<vector<int>> adj(n + 1);
    for(int i = 0; i < m; i++){
        cin >> c1 >> c2;
        adj[c1].push_back(c2);
        adj[c2].push_back(c1);
    }
    int k = 0;
    vector<pair<int, int>> new_road;
    for(int i = 0; i < n; i++){
        if(!visited[i]){
            dfs(i, visited, adj);
        }
        else{
            if(i != 0){
                new_road.push_back(pair<int, int> (i, i+1));
                ++k;
            }
        }
    }
    cout << k << endl;
    for(int i = 0; i < new_road.size(); i++){
        cout << new_road[i].first << ' ' << new_road[i].second << endl;
    }
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: WRONG ANSWER