HashSet<Integer> points = graph.values().stream().flatMap(List::stream).collect(Collectors.toCollection(HashSet::new));
            points.addAll(graph.keySet());
            if (start.equals(goal)) return new SimpleEntry<>(start, null);

            HashMap<Integer, Boolean> visited = new HashMap<>();
            LinkedList<Integer> queue = new LinkedList<>();

            for (int i = 0; i < points.size(); i++) {
                visited.put(new ArrayList<>(points).get(i), false);
            }

            queue.push(start);
            visited.put(start, true);
            while (!queue.isEmpty()) {
                start = queue.pop();
                System.out.print(start + " ");

                List<Integer> neighbours = graph.get(start);
                if (neighbours == null) {
                    continue;
                }

                for (Integer neighbour : neighbours) {
                    if (!visited.get(neighbour)) {
                        visited.put(neighbour, true);
                        queue.push(neighbour);
                    }
                }
            }
            return new SimpleEntry<>(start, new ArrayList<>(visited.keySet()));

        }