Building Teams

#include <iostream>
#include <unordered_set>
#include <unordered_map>

void add_friends(int pupil, const std::unordered_map<int, std::unordered_set<int>> &friendships, std::unordered_set<int>& group_friends){
    if(group_friends.contains(pupil)){
        return;
    }
    //first, add the current pupil
    group_friends.insert(pupil);
    //then, add this pupils friends
    if(friendships.contains(pupil)){
        for (const auto & pupil_friend : friendships.at(pupil)){
            // group_friends.insert(pupil);
            add_friends(pupil_friend, friendships, group_friends);
        }
    }
}

int main(){
    int num_pupils, num_frendships;
    std::unordered_map<int, std::unordered_set<int>> friendships{};
    std::cin >> num_pupils;
    std::cin >> num_frendships;
    for(int i=0; i<num_frendships; i++){
        int friend1, friend2;
        std::cin >> friend1 >> friend2;
        friendships[friend1].insert(friend2);
    }
    std::unordered_set<int> group1, group2;
    std::unordered_set<int> group1_friends, group2_friends;


    // now, we'll add the first pupil into the first group
    // and then iterate over the rest and add them to the 1st one if they have no friends there
    // and if no, then we add them to the second one, if they also have no friends there
    // ughhhh but I know this is so no optimal fuck
    for(int pupil = 1; pupil<= num_pupils; pupil++){
        if(!group1_friends.contains(pupil)){
            group1.insert(pupil);
            add_friends(pupil, friendships, group1_friends);
        }
        else if(not group2_friends.contains(pupil)){
            group2.insert(pupil);
            add_friends(pupil, friendships, group2_friends);
        } else {
            std::cout << "IMPOSSIBLE";
            break;
        }
    }
    for(int i=1; i<=num_pupils; i++){
        std::cout << (group1.contains(i) ? "1" : "2" ) << " ";
    }
    std::cout << "\n";

}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

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