Performing Breadth First Search recursively

Question

Let\'s say you wanted to implement a breadth-first search of a binary tree recursively. How would you go about it?

Is it possible using only the call-stack

Answer 1

I couldn't find a way to do it completely recursive (without any auxiliary data-structure). But if the queue Q is passed by reference, then you can have the following silly tail recursive function:

BFS(Q)
{
  if (|Q| > 0)
     v <- Dequeue(Q)
     Traverse(v)
     foreach w in children(v)
        Enqueue(Q, w)    

     BFS(Q)
}