#BFS

841. Keys and Rooms(#1 ).java

class Solution {
    int count = 0;
    int N = 0;
    public boolean canVisitAllRooms(List<List<Integer>> rooms) {
        if (rooms == null || rooms.size() < 1) return true;
        int n = rooms.size();
        count = n;
        N = n;
        boolean[] visited = new boolean[n];
        Set<Integer> canReach = new HashSet<>();
        visited[0] = true;
        canReach.add(0);
        Queue<Integer> q = new LinkedList<>();
        q.offer(0);
        while (!q.isEmpty()) {
            int cur = q.poll();
            visited[cur] = true;
            canReach.add(cur);
            if (canReach.size() == N) {
                return true;
            }
            for (int i : rooms.get(cur)) {
                if (!visited[i]) {
                    q.offer(i);
                }
            }
            
        }
        return false;
    }
}