Building Teams

#include "iostream"
#include "vector"
#include "map"

int main() {
    int n, m;
    std::cin >> n >> m;
    std::map<int, std::vector<int>> friendships;
    int a, b;
    for (int i = 0; i < m; i++) {
        std::cin >> a >> b;
        try {
            friendships.at(a).push_back(b);
        } catch (...) {
            friendships.insert_or_assign(a, std::vector<int>{b});
        }
        try {
            friendships.at(b).push_back(a);
        } catch (...) {
            friendships.insert_or_assign(b, std::vector<int>{a});
        }
    }
    std::vector<int> teams(n, 0);
    int curr = 1;
    int currTeam = 1;
    while(curr < n) {
        if (teams[curr - 1] != 0) {
            curr++;
            continue;
        }
        teams[curr - 1] = currTeam;
        for (auto& friends : friendships.at(curr)) {
            if (teams[friends - 1] == 0) teams[friends - 1] = 1 + (currTeam==1);
            else if (teams[friends - 1] == currTeam) {
                std::cout << "IMPOSSIBLE";
                return EXIT_FAILURE;
            }
        }
        currTeam = 1 + (currTeam==1);
        curr++;
    }
    for (auto& team : teams) {
        std::cout << team << " ";
    }
}

Test 1

Verdict: RUNTIME ERROR

Test 2

Verdict: RUNTIME ERROR

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: RUNTIME ERROR

Test 6

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at

Test 7

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at

Test 8

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at

Test 9

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at

Test 10

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: RUNTIME ERROR