Connect cities

input/code.cpp: In function 'int main()':
input/code.cpp:80:21: warning: loop variable 'p' creates a copy from type 'const std::pair<long long int, long long int>' [-Wrange-loop-construct]
   80 |     for (const auto p : pps)
      |                     ^
input/code.cpp:80:21: note: use reference type to prevent copying
   80 |     for (const auto p : pps)
      |                     ^
      |                     &

#include<iostream>
#include<queue>
#include <unordered_map>
#include <set>
#include <utility>

typedef long long ll;
using namespace std;

bool dfs(ll a, ll b, unordered_map<ll, set<ll>> &dp, set<ll> &visited)
{
    if (dp[a].find(b) != dp[a].end())
    {
        return true;
    }
    else
    {
        visited.insert(a);
        for (const auto e : dp[a])
        {   
            if (visited.find(e) == visited.end())
            {
                if (dfs(e, b, dp, visited))
                {
                    return true;
                }
            }
        }
        return false;
    }
}

int main()
{   
    ll cities, roads;

    cin >> cities >> roads;

    unordered_map<ll, set<ll>> dp;

    ll a, b;

    while (cin >> a >> b)
    {
        if (dp.find(a) != dp.end())
        {
            dp[a].insert(b);
        }
        else
        {
            dp[a] = {b};
        }

        if (dp.find(b) != dp.end())
        {
            dp[b].insert(a);
        }
        else
        {
            dp[b] = {a};
        }
    }

    ll new_roads = 0;
    vector<pair<ll, ll>> pps;

    for (int i = 2; i <= cities; ++i)
    {   
        set<ll> visited = {};
        if (!dfs(1, i, dp, visited))
        {   
            dp[1].insert(i);
            ++new_roads;
            pps.emplace_back(make_pair(1, i));
        }
    }

    std::cout << new_roads << '\n';

    for (const auto p : pps)
    {
        cout << p.first << " " << p.second << '\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: 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: ACCEPTED