public static void main(String[] args) {
   TreeNode t1 = new TreeNode(5);
   TreeNode t2 = new TreeNode(4);
   TreeNode t3 = new TreeNode(8);
   TreeNode t4 = new TreeNode(11);
   TreeNode t5 = new TreeNode(13);
   TreeNode t6 = new TreeNode(4);
   TreeNode t7 = new TreeNode(7);
   TreeNode t8 = new TreeNode(2);
   TreeNode t9 = new TreeNode(1);
   t1.left = t2;
   t1.right = t3;
   t2.left = t4;
   t3.left = t5;
   t3.right = t6;
   t4.left = t7;
   t4.right = t8;
   t6.right = t9;
   System.out.println(levelOrderBottom(t1));
 }
  private TreeNode buildTree(int[] inorder, int[] preorder, int start, int end) {
    if (end < start) {
      return null;
    }

    TreeNode root = new TreeNode(preorder[preIndex++]);
    if (start == end) {
      return root;
    }

    int inIndex = search(inorder, start, end, root.val);

    root.left = buildTree(inorder, preorder, start, inIndex - 1);
    root.right = buildTree(inorder, preorder, inIndex + 1, end);
    return root;
  }
  public static void main(String[] args) {
    TreeNode root = new TreeNode(1);
    root.left = new TreeNode(2);
    root.right = new TreeNode(2);

    root.left.left = new TreeNode(3);
    root.left.right = new TreeNode(3);

    root.right.left = new TreeNode(4);
    root.right.right = new TreeNode(3);

    List<List<Integer>> res = levelOrder(null);

    for (List<Integer> r : res) {
      for (int i : r) {
        System.out.print(i + "\t");
      }
      System.out.println();
    }
  }
 private List<TreeNode> generate(int start, int end) {
   List<TreeNode> list = new ArrayList<TreeNode>();
   if (start <= end) {
     for (int i = start; i <= end; i++) {
       List<TreeNode> left = generate(start, i - 1);
       List<TreeNode> right = generate(i + 1, end);
       int leftSize = left.size();
       int rightSize = right.size();
       for (int p = 0; p < leftSize; p++) {
         for (int q = 0; q < rightSize; q++) {
           TreeNode node = new TreeNode(i);
           node.left = left.get(p);
           node.right = right.get(q);
           list.add(node);
         }
       }
     }
   } else list.add(null);
   return list;
 }