Interview Question for Analyst at Goldman Sachs:

print element from a binary tree in order: (we need to use a queue helper, like in BFS)

public void printTreeInOrder(Tree t)
{
    Queue<Tree> q = new Queue<Tree>();
    if (t!=null)
    {
        q.offer(t); //push tree to the queue
    }
    printTreeHelper(q);
}

public void printTreeHelper(Queue<E> q)
{
    if ((Tree t = q.poll)!=null)
    {
        system.out.println(t.val);
        q.offer(t.left); //push left son
        q.offer(t.right) // push right son
        printTreeHelper(q); //recursive call
    }

}