class Solution {
    public Node connect(Node root) {

        if(root==null)
            return root;

        Queue<Node> queue = new LinkedList<>();

        queue.add(root);


        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i=0; i<size; i++){
               Node node = queue.remove();

               if(i<size-1)
               node.next = queue.peek();

              if(node.left != null)
                  queue.add(node.left);

               if(node.right!=null)
                  queue.add(node.right);

            }
        }

        return root;
    }
}