Connect cities

#include <iostream>
#include <list>
using namespace std;

class city
{
private:
list<city> connected;
public:
    bool been = false;
    city(){};
    ~city(){};

    void connect(city& other) {
        connected.push_back(other);
        other.connected.push_back(*this);
    };

    void visitGroup() {
        if (been) return;
        been = true;
        for (auto c: connected) {
            c.visitGroup();
        }
    }
};

int main() {
    int n, m;
    cin >> n >> m;
    city* cities = new city[n];

    for (int i=0; i<m; i++) {
        int a, b;
        cin >> a >> b;
        cities[a].connect(cities[b]);
    }

    list<int> groups;
    for (int i=0; i<n; i++) {
        if (!cities[i].been) {
            groups.push_back(i);
            cities[i].visitGroup();
        }
    }
    cout << groups.size() - 1 << endl;

    for (auto i=groups.begin(); i!=groups.end(); i++) {
        cout << *groups.begin() + 1 << " " << *i + 1 << endl;
    }

    delete cities;
    return 0;
}

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

Test 7

Verdict: RUNTIME ERROR

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: RUNTIME ERROR

Test 10

Verdict: RUNTIME ERROR

Test 11

Verdict: RUNTIME ERROR

free(): invalid pointer

Test 12

Verdict: RUNTIME ERROR