Connect cities

#include <string>
#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <unordered_set>


using namespace std;

int main()
{
    int n_cities;
    int n_roads;
    cin >> n_cities >> n_roads;

    map<int, unordered_set<int>> city_map;
    map<int, bool> cities_with_roads;

    int road1, road2;

    for(int i = 0; i < n_roads; i++)
    {
        bool in = false;
        int temp_key;
        cin >> road1 >> road2;

        cities_with_roads[road1] = true;
        cities_with_roads[road2] = true;
        for(auto & [key, val] : city_map)
        {
            if(val.find(road1) != val.end() || val.find(road2) != val.end())
            {
                val.insert(road1);
                val.insert(road2);
                if(!in) temp_key = key, in = true;
                else
                {
                    city_map[temp_key].merge(val);
                    city_map.erase(key);
                    break;
                }
            }
        }
        if(!in)
        {
            unordered_set<int> temp = {road1, road2};
            city_map[road1] = temp;
        }
    }
    for(int i = 1; i <= n_cities; i++)
    {
        if(!cities_with_roads.count(i))
        {
            city_map[i] = {i};
        }
    }
    printf("%ld\n", city_map.size() - 1);
    map<int, unordered_set<int>>::iterator it1;
    map<int, unordered_set<int>>::iterator it2 = city_map.begin();
    it2++;
    for(it1 = city_map.begin(); it2 != city_map.end(); ++it1, ++it2)
    {
        printf("%d %d\n", *(it1->second.begin()), *(it2->second.begin()));
    }

}   

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

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: ACCEPTED

Test 12

Verdict: ACCEPTED