public static int journeyToMoon(int n, List<List<Integer>> astronaut) {
        // Write your code here
        Map<Integer, List<Integer>> adj = buildAdjList(n, astronaut);

        Set<Integer> visited = new HashSet<>();
        Set<Set<Integer>> countries = new HashSet<>();
        for (int i=0;i<n;i++) {
            if (!visited.contains(i)) {
                Set<Integer> astronautInCountry = new HashSet<>();
                
                dfsVisit(adj, i, visited, astronautInCountry);
                
                countries.add(astronautInCountry);
            }
        }
        long result = 0;
        for (Set<Integer> country : countries) {
				// If choose 1st atronaut from country, there are (n - country.size()) astronaut to choose 2nd.
            result += (country.size() * (n - country.size()));
        }
        return (int)(result / 2);
    }
    
    private static void dfsVisit(final Map<Integer, List<Integer>> adj, int node, Set<Integer> visited, Set<Integer> astronautInCountry) {
        visited.add(node);
        astronautInCountry.add(node);
        
        for (int neighbor : adj.get(node)) {
            if (!visited.contains(neighbor)) {
                dfsVisit(adj, neighbor, visited, astronautInCountry);
            }
        }
    }
    
    private static Map<Integer, List<Integer>> buildAdjList(int n, List<List<Integer>> astronaut) {
        Map<Integer, List<Integer>> adj = new HashMap<>();
        
        for (int i=0; i<n; i++) {
            adj.put(i, new ArrayList<>());
        }
        for (List<Integer> edge : astronaut ) {
            adj.get(edge.get(0)).add(edge.get(1));
            adj.get(edge.get(1)).add(edge.get(0));
        }
        
        return adj;
    }