815. Bus Routes

class Solution {
    public int numBusesToDestination(int[][] routes, int source, int target) {
        Map<Integer, List<Integer>> stopToRouteMap = new HashMap<>();
        for (int i = 0; i < routes.length; i++) {
            for (int j = 0; j < routes[i].length; j++) {                
                if (!stopToRouteMap.containsKey(routes[i][j])) {
                    stopToRouteMap.put(routes[i][j], new ArrayList<>());
                }
                stopToRouteMap.get(routes[i][j]).add(i);
            }
        }
        if (!stopToRouteMap.containsKey(source)) {
            return -1;
        }
        // [[1,2,7],[3,6,7]]
        // 1: 0
        // 2: 0
        // 3: 1
        // 6: 2
        // 7: 1,2
        Queue<Integer> queue = new LinkedList<>();
        queue.offer(source);
        Set<Integer> stopVisited = new HashSet<>();
        Set<Integer> routeVisited = new HashSet<>();
        stopVisited.add(source);
        int numOfBuses = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                int curStop = queue.poll();
                if (curStop == target) {
                    return numOfBuses;
                }
                if (stopToRouteMap.containsKey(curStop)) {
                    List<Integer> curRoutes = stopToRouteMap.get(curStop);
                    for (int route : curRoutes) {
                        if (routeVisited.contains(route)) {
                            continue;
                        }
                        routeVisited.add(route);
                        int[] stops = routes[route];
                        for (int stop : stops) {
                            if (!stopVisited.contains(stop)) {
                                queue.offer(stop);
                                stopVisited.add(stop);
                            }
                        }
                    }
                }
            }
            numOfBuses ++;
        }
        return -1;
    }
}