Josh Haverford

Stephan van Hulst wrote:Yes, you will have to repeat the process for the right leaf. Also, if the left or right node you are considering is not a leaf, it means it is a root of a subtree, which contains leaves you may want to delete.

I might as well show you the final solution now. Let us know whether you understand it.
public static void deleteLeaves(BSTNode root) { if (isLeaf(root.left)) root.left = null; else deleteLeaves(root.left); if (isLeaf(root.right)) root.right = null; else deleteLeaves(root.right); }

[edited 10.000 times for typos, arghghgh]

Let me get this right, so in the else statement, deleteLeaves(root.left, right) is just going to the next node making the one just checked its parent if the left/right has no children(meaning it is not a leaf), and then checking the child of that?

Im getting a Null pointer exception when i call the deleteleaves method in my main
deleteLeaves(tree.root);


am i calling it right? how do i show that they have been deleted correctly?



Also, this may sound like a stupid question, but is the height of this tree 5? I dont think my height code is working properly
35 30 27 26 25 23 20 15 10

Stephan van Hulst wrote:I'll start you off:
public void deleteLeaves(BSTNode root) { if (isLeaf(root.left)) root.left = null; else // }

dont i need to set the right side to null as well?


for what to put after the else statement, if it is not null i have it return and quit?

Paul Clapham wrote:I'm confused about what you expect that line of code to do:
deleteLeaves(test.next = null);
What that does (or would do if it compiled) is this:

Assign null to the test.next variable

Call deleteLeaves(null)

Personally I wouldn't write that line of code, since it's rather obscure. If I wanted to do those two things I would write the appropriate two lines of code to do them. (But I suspect you don't quite want to do those two things.)

Yeah, i realize what i have to do. I need to test whether a node is a leaf from its parent so that the
reference to this leaf can be set to null, which deletes the leaf, but i dont understand the proper code to implement that. I am a first year java student. I know there are so many options out there but i feel so limited due to my lack of experience and knowledge..

// e. to delete all leaves from a binary tree public static boolean isLeaf(BSTNode test) { if ((test.left == null) && (test.right == null)) return true; else return false; } public static void deleteLeaves(BSTNode test) { if (isLeaf(test)) deleteLeaves(test.next = null); else { deleteLeaves(test.left); deleteLeaves(test.right); } }


How does this look? it is saying next isnt a field, is there another way i am supposed to be looking at the child node from the parent ?

public static void delete(BSTNode test) { if ((test.left != null) && (test.right != null)) { delete(test.left); delete(test.right); } }


so your saying that code?


I thought leaves meant there were no children ie. empty


I think i need a depth-first traversal

// e. to delete all leaves from a binary tree public static void delete(BSTNode test) { if ((test.left == null) && (test.right == null)) delete(test = null); ///test.current element??? not whole test tree }

i am having trouble doing this - any suggestions?