Simple BFS Traversal using C++

#include <bits/stdc++.h>

using namespace std;

/**

    Use this as input: (copy-paste in terminal)

    3
    4 2
    1 2
    2 3
    5 3
    1 2
    2 3
    1 3
    6 3
    1 2
    3 4
    5 6

*/

vector<vector<int>> a;
vector<bool> visited;
int cnt = 0;

void BFS(int u) {
    queue<int> q;
    visited[u] = true;
    q.push(u);
    while (!q.empty()) {
        u = q.front();
        q.pop();
        for (auto it = a[u].begin(); it != a[u].end(); it++) {
            if (!visited[*it]) {
                visited[*it] = true;
                q.push(*it);
                cout << " -> " << *it + 1;
            }
        }
    }
}

int main() {
    int tt;
    cin >> tt;
    while (tt--) {
        int n, m;
        cin >> n >> m;
        a = vector<vector<int>>(n);
        for (int i = 0; i < m; i++) {
            int u, v;
            cin >> u >> v;
            --u, --v;
            a[u].push_back(v);
            a[v].push_back(u);
        }
        visited = vector<bool>(n, false);
        for (int u = 0; u < n; u++) {
            if (!visited[u]) {
                cout << u + 1;
                BFS(u);
                cout << '\n';
            }
        }
        cout << "----\n";
    }
    return 0;
}