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POBuild binary expression tree from prefix notation?
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copied!<pre><code>import java.util.ArrayList; import java.util.List; public class ExpressionTree { List<String> expArray = new ArrayList<String>(); ExpressionTreeNode root; ExpressionTreeNode curNode; ExpressionTreeNode left; ExpressionTreeNode right; String element; public ExpressionTree(String prefixExpression) { String[] temp = prefixExpression.split(" "); for (int i = 0; i < temp.length; i++) { expArray.add(temp[i]); } root = createExpressionTree(expArray); System.out.println(root); } private ExpressionTreeNode createExpressionTree(List<String> prefixExpression) { element = prefixExpression.get(0); prefixExpression.remove(0); if (isNumeric(element)) { return new Leaf(Double.parseDouble(element)); } else { left = createExpressionTree(prefixExpression); right = createExpressionTree(prefixExpression); } return new ExpressionTreeNode(left, right, element); } private static boolean isNumeric(String str) { try { double d = Double.parseDouble(str); } catch(NumberFormatException nfe) { return false; } return true; } } </code></pre> <p>That is my code that I want to return an expression tree when given an expression like * + 5 4 – 3 / 2 1. The output i'm getting though is something like this:</p> <pre><code>1 |\ 2 1 /\ 2 1 /\ 2 1 </code></pre> <p>When I'm trying to get:</p> <pre><code> * /\ + - /\ /\ 5 4 3 / /\ 2 1 </code></pre> <p>Any tips? Why are the only elements of my tree the last two elements of the expression? I feel like I'm missing something obvious.</p>

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