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POJava recursion: pass by reference
 

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    <p>I realize this is a hotly debated, controversial topic for Java programmers, but I believe my problem is somewhat unique. My algorithm <strong>REQUIRES</strong> pass by reference. I am doing a clockwise/counterclockwise pre-order traversal of a general tree (i.e. n-children) to assign virtual (x,y) coordinates. This simply means I count (and tag) the nodes of tree I visit as I visit them.</p> <pre><code>/** * Generates a "pre-ordered" list of the nodes contained in this object's subtree * Note: This is counterclockwise pre-order traversal * * @param clockwise set to true for clockwise traversal and false for counterclockwise traversal * * @return Iterator&lt;Tree&gt; list iterator */ public Iterator&lt;Tree&gt; PreOrder(boolean clockwise) { LinkedList&lt;Tree&gt; list = new LinkedList&lt;Tree&gt;(); if(!clockwise) PreOCC(this, list); else PreO(this,list); count = 0; return list.iterator(); } private void PreOCC(Tree rt, LinkedList&lt;Tree&gt; list) { list.add(rt); rt.setVirtual_y(count); count++; Iterator&lt;Tree&gt; ci = rt.ChildrenIterator(); while(ci.hasNext()) PreOCC(ci.next(), list); } private void PreO(Tree rt, LinkedList&lt;Tree&gt; list, int count) { list.add(rt); rt.setX_vcoordinate(count); Iterator&lt;Tree&gt; ci = rt.ReverseChildrenIterator(); while(ci.hasNext()) PreO(ci.next(), list, ++count); } </code></pre> <p>Here I generate the structure of the tree:</p> <pre><code>Tree root = new Tree(new Integer(0)); root.addChild(new Tree(new Integer(1), root)); root.addChild(new Tree(new Integer(2), root)); root.addChild(new Tree(new Integer(3), root)); Iterator&lt;Tree&gt; ci = root.ChildrenIterator(); ci.next(); Tree select = ci.next(); select.addChild(new Tree(new Integer(4), select)); select.addChild(new Tree(new Integer(5), select)); </code></pre> <p>And here is my output when I print the order the nodes are traversed and the coordinates it assigns to the respective node.</p> <p><code>0 3 2 5 4 1</code><br> <code>0 1 2 3 4 3</code> </p> <p><code>0 1 2 4 5 3</code><br> <code>0 1 2 3 4 3</code></p> <p><em>Note: The first two lines is a clockwise pre-order traversal and assignment of the x-coordinates. The next two lines are a counterclockwise pre-order traversal and assignment of they y-coordinates.</em></p> <p>My question is how I can get the second lines to read: <code>0 1 2 3 4 5</code></p> <p>EDIT 1: Here is the code I use to print the order I visit the nodes and the coordinates I assign.</p> <pre><code>Iterator&lt;Tree&gt; pre = root.PreOrder(true); System.out.println(" \t"); while(pre.hasNext()) System.out.print(pre.next() + "\t"); pre = root.PreOrder(true); System.out.println(); System.out.println("x-coordinates:\t"); while(pre.hasNext()) System.out.print(pre.next().getVirtual_x() + "\t"); System.out.println(); System.out.println(); Iterator&lt;Tree&gt; preCC = root.PreOrder(false); System.out.println(" \t"); while(preCC.hasNext()) System.out.print(preCC.next() + "\t"); preCC = root.PreOrder(false); System.out.println(); System.out.println("x-coordinates:\t"); while(preCC.hasNext()) System.out.print(preCC.next().getVirtual_y() + "\t"); </code></pre> <p>Also here is a quote to better explain the x,y coordinates. the vertices.the y-coordinates for the vertices.</p> <blockquote> <p>Compute the counterclockwise pre-ordering of the vertices of T (the ordering are numbered from 0 to n − 1), use them as the x-coordinates for the vertices. </p> <p>Compute the clockwise pre-ordering of the vertices of T (the ordering are numbered from 0 to n − 1), use them as the y-coordinates for the vertices.</p> </blockquote>
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    1. USNathan
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    1. COSo controversial....
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    2. COI agree. Which makes it even harder to understand what to do here!
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      1. USNathan
    3. CONathan are you sure the Tree you are constructing has the structure you intend? I don't see how a pre-order traversal of the nodes would visit them in the order of 012345.
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