Slog Week8

    This week we were still working on trees, especially Binary trees that have two children, left and right. We focused on different orders to visit nodes through a tree. The professor introduced us three different orders to visit the tree and the one that I felt confused with is level order. The following is an example:

def visit_level(t, n, act):

      """

   Visit each node of BinaryTree t at level n and act on it.  Return
   the number of nodes visited visited.

   """

   if t is None:

       return 0

   elif n == 0:

       return 1

   else:

       return (visit_level(t.left, n-1, act) + 

               visit_level(t.right, n-1, act)

I'm struggling with the else part. I don't understand why it should be n-1 but not n instead. if n = 1, aren't we visit the tree at level 0? I guess the outcome would be 2 but not 3 as we expected. 

    Also, term test two is coming, and we have assignment two to due by two weeks. Hopefully I will be well prepared for the upcoming test and get started for the assignment.