Print Binary Tree

  static class BTreePrinter {

    public static <T extends Comparable<?>> void printNode(Node root) {
      int maxLevel = BTreePrinter.maxLevel(root);

      printNodeInternal(Collections.singletonList(root), 1, maxLevel);
    }

    private static <T extends Comparable<?>> void printNodeInternal(List<Node> nodes, int level, int maxLevel) {
      if (nodes.isEmpty() || BTreePrinter.isAllElementsNull(nodes))
        return;

      int floor = maxLevel - level;
      int endgeLines = (int) Math.pow(2, (Math.max(floor - 1, 0)));
      int firstSpaces = (int) Math.pow(2, (floor)) - 1;
      int betweenSpaces = (int) Math.pow(2, (floor + 1)) - 1;

      BTreePrinter.printWhitespaces(firstSpaces);

      List<Node> newNodes = new ArrayList<>();
      for (Node node : nodes) {
        if (node != null) {
          System.out.print(node.item.getId());
          newNodes.add(node.left);
          newNodes.add(node.right);
        } else {
          newNodes.add(null);
          newNodes.add(null);
          System.out.print(" ");
        }

        BTreePrinter.printWhitespaces(betweenSpaces);
      }
      System.out.println("");

      for (int i = 1; i <= endgeLines; i++) {
        for (int j = 0; j < nodes.size(); j++) {
          BTreePrinter.printWhitespaces(firstSpaces - i);
          if (nodes.get(j) == null) {
            BTreePrinter.printWhitespaces(endgeLines + endgeLines + i + 1);
            continue;
          }

          if (nodes.get(j).left != null)
            System.out.print("/");
          else
            BTreePrinter.printWhitespaces(1);

          BTreePrinter.printWhitespaces(i + i - 1);

          if (nodes.get(j).right != null)
            System.out.print("\\");
          else
            BTreePrinter.printWhitespaces(1);

          BTreePrinter.printWhitespaces(endgeLines + endgeLines - i);
        }

        System.out.println("");
      }

      printNodeInternal(newNodes, level + 1, maxLevel);
    }

    private static void printWhitespaces(int count) {
      for (int i = 0; i < count; i++)
        System.out.print(" ");
    }

    private static <T extends Comparable<?>> int maxLevel(Node node) {
      if (node == null)
        return 0;

      return Math.max(BTreePrinter.maxLevel(node.left), BTreePrinter.maxLevel(node.right)) + 1;
    }

    private static <T> boolean isAllElementsNull(List<T> list) {
      for (Object object : list) {
        if (object != null)
          return false;
      }

      return true;
    }

  }