GfG.java

class GfG{
    boolean isLeaf(Node node){
        return node.left==null && node.right==null;
    }
    boolean isComplete(Node node){
        return node.left!=null && node.right!=null;
    }
    boolean isEmptyLeftButFullRight(Node node){
        return node.left==null && node.right!=null;
    }
	boolean isCompleteBT(Node root){
        Queue<Node> q = new LinkedList<>();
        q.add(root);
        boolean flag = false;
        while(q.size()!=0){
            Node current = q.poll();
            
            if(flag && !isLeaf(current)) return false;
            if(!isComplete(current)) flag = true;
            if(isEmptyLeftButFullRight(current)) return false;
            if(current.left!=null) q.add(current.left);
            if(current.right!=null) q.add(current.right);
        }
        return true;
	} 
}