TreeNextPointer.java

class Solution {
    public Node connect(Node root) {
       
        if(root == null) return null;
         Queue<Node> queue = new LinkedList();
       queue.add(root);
        
        
        while(queue.size()>0){
            int size = queue.size();
            
            for(int i=0;i<size; i++){
                
                Node node = queue.poll();
                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;
        
    }
}