Connect cities

#include "iostream"
#include "vector"
#include "map"
#include "list"
#include "algorithm"

// int main() {
//     int n, m;
//     std::cin >> n >> m;
//     if (1 > n || n > 100000 || 1 > m || m > 200000) return EXIT_FAILURE;
//     std::vector<std::vector <int>> roads = {};
//     std::vector<std::vector<bool>> adjacenceMatrix(n, std::vector<bool>(n, false));
//     int a, b;
//     for (int i = 1; i <= m; i++) {
//         std::cin >> a >> b;
//         if ((1 <= a) && (a <= n) && (1 <= b) && (b <= n)) {
//             roads.push_back(std::vector<int>{a, b});
//             adjacenceMatrix[a-1][b-1] = true;
//             adjacenceMatrix[b-1][a-1] = true;
//         }
//     }
//     std::vector<int> neighbors = {1};
//     int k = 0;
//     std::vector<std::vector<int>> newRoads = {};
//     std::vector<bool> notVisited(n + 1, true);
//     notVisited[0].flip();
//     while (!neighbors.empty() && !notVisited[0]) {
//         int curr = neighbors.back();
//         neighbors.pop_back();
//         if (!notVisited[curr]) continue;
//         notVisited[curr] = false;
//         for (int roadIdx = 0; roadIdx < m;) {
//             int front = roads[roadIdx].front();
//             int back = roads[roadIdx].back();
//             bool erasure = false;
//             if (adjacenceMatrix[front - 1][curr - 1] && notVisited[front]) {
//                 notVisited[front] = false;
//                 neighbors.push_back(front);
//                 roads.erase(roads.begin() + roadIdx);
//                 erasure = true;
//             }
//             if (adjacenceMatrix[back - 1][curr - 1] && notVisited[back]) {
//                 notVisited[back] = false;
//                 neighbors.push_back(back);
//                 roads.erase(roads.begin() + roadIdx);
//                 erasure = true;
//             }
//             roadIdx, m = (erasure) ? roadIdx, m - 1 : roadIdx + 1, m;
//         }
//         if (neighbors.empty()) {
//             int city = 1;
//             while (city <= n) {
//                 if (notVisited[city]) {
//                     neighbors.push_back(city);
//                     k++;
//                     newRoads.push_back(std::vector<int>{curr, city});
//                     adjacenceMatrix[curr - 1][city - 1] = true;
//                     adjacenceMatrix[city - 1][curr - 1] = true;
//                     break;
//                 }
//                 city++;
//             }
//             if (city > n) notVisited[0] = true;
//         }
//     }

//     std::cout << k << std::endl;
//     for (int i = 0; i < k; i++) {
//         std::cout << newRoads[i].front() << " " << newRoads[i].back() << std::endl;
//     }
// }

int main() {
    int n, m;
    std::cin >> n >> m;
    std::map<int, std::vector<int>> connections;
    int a, b;
    for (int i = 0; i < m; i ++) {
        std::cin >> a >> b;
        connections[a].push_back(b);
        connections[b].push_back(a);
    }
    std::vector<int> visited;
    std::vector<int> heads;
    for (int i = 1; i <= n; i++) {
        auto node = find(visited.begin(), visited.end(), i);
        if (node == visited.end()) {
            visited.push_back(i);
            heads.push_back(i);
        }
        sort(connections[i].begin(), connections[i].end());
        for (int elem : connections[i]) {
            visited.push_back(elem);
        }
    }
    int k = heads.size() - 1;
    std::cout << k << std::endl;
    for (int i = 0;  i < k; i++) {
        std::cout << heads[i] << " " << heads[i+1] << std::endl;
    }
}

Test 1

Verdict: ACCEPTED

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: ACCEPTED