Keys_And_Rooms.java

class Solution {
    public boolean canVisitAllRooms(List<List<Integer>> rooms) {
        HashSet<Integer>visited=new HashSet<>();
        visited.add(0);
        Stack<Integer> stack =new Stack<>();
        stack.add(0);
        while(!stack.isEmpty())
        {
            List<Integer>keys=rooms.get(stack.pop());
            for (int key:keys)
            {
                if(!visited.contains(key))
                {
                    visited.add(key);
                    stack.add(key);
                }
            }
        }
        return visited.size()==rooms.size();
    }
}