Connect cities

In file included from /usr/include/c++/11/bits/stl_tree.h:65,
                 from /usr/include/c++/11/set:60,
                 from input/code.cpp:1:
/usr/include/c++/11/bits/stl_function.h: In instantiation of 'constexpr bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::unordered_set<unsigned int>]':
/usr/include/c++/11/bits/stl_tree.h:2071:35:   required from 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = std::unordered_set<unsigned int>; _Val = std::unordered_set<unsigned int>; _KeyOfValue = std::_Identity<std::unordered_set<unsigned int> >; _Compare = std::less<std::unordered_set<unsigned int> >; _Alloc = std::allocator<std::unordered_set<unsigned int> >; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::key_type = std::unordered_set<unsigned int>]'
/usr/include/c++/11/bits/stl_tree.h:2124:4:   required from 'std::pa...

#include <set>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <unordered_set>

std::unordered_set<uint32_t> find_in_set(std::set<std::unordered_set<uint32_t>> s, uint32_t to_find){
    auto r= s.begin();
    for (; r != s.end() && ! (*r).contains(to_find); r++);
    return *r;
}

int main() {
    uint32_t n = 0;
    uint32_t m = 1;
    if (scanf("%d %d", &n, &m) == 0)
        return EXIT_FAILURE;

    std::set<std::unordered_set<uint32_t>> s;
    for (uint32_t i = 0; i < n; i++){
        s.insert({i});
    }


    // main algo

    uint32_t x, y;
    std::unordered_set<uint32_t> sx, sy;
    sx = *s.begin();
    for(uint32_t i = 0; i < m; i++){
        if (scanf("%d %d", &x, &y) == 0)
            return EXIT_FAILURE;
        
        sx = find_in_set(s, x);
        if (! sx.contains(y)){
            sy = find_in_set(s, y);
            s.erase(sy);
            sx.merge(sy);
        }
    }
    printf("%ld\n", s.size());
    if (s.size() > 1){
        s.erase(sx);
        for (auto r = s.begin(); r != s.end(); r++){
            printf("%d %d", *sx.begin(), *sy.begin());
        }
    }


    return EXIT_SUCCESS;
}