Leetcode 841. Keys and Rooms

class Solution {
    public boolean canVisitAllRooms(List<List<Integer>> rooms) {
        if(rooms == null || rooms.size() == 0) {
            return true;
        }

        int n = rooms.size();

        int visitedCount = 1;
        boolean[] visited = new boolean[n];
        visited[0] = true;

        Queue<Integer> q = new LinkedList<Integer>();
        for(int nextKey : rooms.get(0)) {
            if(!visited[nextKey]) {
                q.add(nextKey);
                visited[nextKey] = true;
                visitedCount++;
            }
        }

        while(visitedCount < n && !q.isEmpty()) {
            int key = q.remove();
            for(int nextKey : rooms.get(key)) {
                if(!visited[nextKey]) {
                    q.add(nextKey);
                    visited[nextKey] = true;
                    visitedCount++;
                }
            }
        }
        return visitedCount == n;
    }
}