Subj : Re: Recursion in Java: Question for those who understand recursion well.
To   : comp.programming
From : CBFalconer
Date : Sat Aug 27 2005 08:34 am

Casey Hawthorne wrote: (carelessly neglecting to include context)
> success_ny@yahoo.com wrote:           (which I have reinserted)
>> 
>> I have a tree represented as a linked list of simple objects
>> (nodeId/parentId pairs) where the root node is the 1st element in
>> the list. The other nodes are in somewhat random order. The
>> parentId refers to the parent node.
>> 
>> I want to convert it into a list where the values are in pre-order.
>> I.e., I want to get this list as follows: ABCDEFGHIJ (see graph
>> below). I.e., get the 1st node, put in in the list. If it has
>> children, go through them one by one, get their child nodes, then
>> put the parent in the list, then the leftmost first, and go from
>> there. I.e., so that it's ordered in my linked list like this by
>> (letters represent nodeId):
>> 
>>          A
>>         / \
>>        B   J
>>      / | \
>>     C  H  I
>>     |
>>     D
>>    /|\
>>   E F G
>> 
.... snip code ...
>>  
>> Any idea what the problem is? 
> 
> You are doing preorder traversal.
> 
>  preorder(tree)
>  begin
>      if tree is null, return;
> 
>      print(tree.root);
>      preorder(tree.left_subtree);
>      preorder(tree.right_subtree);
>  end

No he isn't.  What he has shown is not a binary tree.  Even if it
was, he would want an inorder traversal.  He neglected to show the
declarations for the actual tree.

For help, the OP should post a complete compilable minimized
program.

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