View difference between Paste ID: ddKXgAZB and 6QMahGAv

 import java.io.*;
 import java.util.*;
 
 public class BinaryTreeTraversal {
 
     /**
      * @param args
      */
     public static void main(String[] args) {
         Scanner input = new Scanner("input.txt");
         int n = input.nextInt();
         int m = (int) Math.pow(2,n)-1;
         List<BinaryNode<Character>> list = new ArrayList<BinaryNode<Character>>();
 
         for (Character c : input.nextLine().toCharArray()) {
             list.add(new BinaryNode<Character>(Character.isLetter(c) ? c : null));
         }
         BinaryNode<Character> root = list.get(0);
 
-        // HERE: turn the flat, unrelated array of BinaryNode's into a real tree starting with root.
+        for (int i = 1; i <= list.size(); i++) {
             BinaryNode<Character> node = list.get(i-1);
             if (node == null)
                 continue;
             node.setLeft(list.get(2*i);
             node.setRight(list.get(2*i+1);
         }
 
         System.out.println(root.toStringPreOrder());
         System.out.println(root.toStringInOrder());
         System.out.println(root.toStringPostOrder());
         // done!
     }
 }