BFS Best Practice

int main() {
	for(int i=1;i<=n;i++) {
		cin >> s >> d;
		arr[s].push_back(d);
	}	
	queue<int> q;	
	while(!q.empty()) {
		const auto cur = q.front(); q.pop();
		cout << cur << " "; // 방문
		for(const auto& nx : arr[cur]) {
			if(vis[nx] == 0) {
				vis[nx] = 1;
				q.push(nx);
			}
		}
	}
	return 0;
}