Connect cities

#include <iostream>
#include <cmath>

#include <string>
#include <vector>
#include <set>
#include <utility>

void    print_graph(std::vector<std::set<int>> graph)
{
    for (size_t i = 0; i < graph.size(); ++i) {
        auto s = graph[i];
        std::cout << "{";
        for (auto it = s.begin(); it != s.end(); ++it) {
            if (it != s.begin())
                std::cout << ", ";
            std::cout << *it;
        }
        std::cout << "} ";
    }
    std::cout << std::endl;
}

int main() {
    int n, m;
    std::cin >> n >> m;

    if (n < 1 || n > 10000)
        return (0);
    if (m < 1 || m > 20000)
        return (0);

    std::set<int> s;
    for (int i = 1; i <= n; ++i)
        s.insert(i);
 

    std::vector<std::set<int>> graph={};
    int a, b;
    for (int i = 0; i < m; i++)
    {
        bool found = false;
        std::cin >> a >> b;
        std::set<int> tmp;
        tmp.insert(a);
        tmp.insert(b);
        if (i == 0)
        {
            graph.push_back(tmp);
        }
        else {
            for (size_t i = 0; i < graph.size(); ++i) {
                if (graph[i].contains(a) || graph[i].contains(b)) {
                    graph[i].insert(a);
                    graph[i].insert(b);
                    found = true;
                    break ;
                }
            }
            if (!found) {
                graph.push_back(tmp);
            }
        }
        // print_graph(graph);
    }

    int count = 0;
    std::vector<std::pair<int, int>> print;
    for (size_t i = 0; i + 1 < graph.size(); ++i) {
        std::set<int> s1 = graph[i];
        std::set<int> s2 = graph[i + 1];
        int begin = *--s1.end();
        int end = *s2.begin();
        for (; begin < end; ++begin) {
            std::pair<int, int> tmp = {begin, begin + 1};
            print.push_back(tmp);
            count++;
        }
    }
    std::cout << count << std::endl;
    for (size_t i = 0; i < print.size(); ++i) {
        std::cout << print[i].first << " " << print[i].second;
        if (i + 1 < print.size())
            std::cout << std::endl;
    }
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: ACCEPTED

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER