Need help printing out a BinarySearchTree

Question

I am trying to write a method to print out a BinarySearchTree, so I can better debug my code. For instance, if the binarysearchtree is in this form:
6
3 9
2 4 12 8
Then I want to print out this exact form using System.out.println. The recursive traversal techniques (inorder, postorder, preorder) do not accomplish this. When I tried to use one of the technique, I got a weird looking tree that either rotate 90 degree or upside down. Any ideas? Thanks

Answer 1

I agree, but I would like to take this opportunity to
learn some new trick too.There isn't any trick. There's just a lot of grungy programming. You have to keep track of how many nodes you're going to display on line 1, line 2, line 3, and so on. And how wide those nodes are. (And "how wide a node is" depends on how wide its children are and whether its neighbours have children or not.) You can't display line 1 until you have laid out the entire tree conceptually, because you don't know how much space to leave to its left so that it is centred above its children.
Now if you've got a complete binary tree (as uj suggested earlier) then this is simple. But if you don't, then it isn't simple at all. Unless, of course, you want to pretend that you do, and just leave space where the missing nodes are. That would be pretty simple. Find the maximum depth of your tree, call that D, and find the maximum width of a node, call that N. Then the bottom level of your tree would be N * 2^D wide (I probably have an off-by-one error in D there so fix that if necessary).
So line 1 has one node, which automatically goes in the middle. If line 2 is the last line then its two nodes go at the right and left ends. If it isn't, but line 3 is going to be the last line, then line 2's nodes go 1/6 and 5/6 of the way across. If there's going to be four lines the line 2's nodes go 3/14 and 11/14 of the way across. (I figured those out by drawing pictures like the examples you posted.) Find the general formula that yields these numbers. Then do the same for line 3 and line N.
(If you want to draw the tree upside-down, it's quite a bit easier. Draw the last line, keeping track of where you draw each node. Then when you draw the next line, each node gets drawn between where you drew its children, recursively.)
This is the simple version we are doing here, remember. You will probably learn a lot by finishing it off, but not a lot about tree structures. The general version is not a generalization of this algorithm, but a completely different algorithm.