public static ExpressionTree toExpressionTree(String[] tokens)
  {
    Stack<ExpressionTree> stk = new Stack<ExpressionTree>();
    for(String token:tokens)
    {
      if(Character.isDigit(token.charAt(0)))
        stk.push(new ExpressionTree(token));
      else
        stk.push(new ExpressionTree(token,stk.pop(),stk.pop()));
    }
    return stk.pop();
  }

////////
public class bststuff
{
  public static void reversePrint(TreeNode root)
  {
    if(root != null)
    {
      reversePrint(root.getRight());
      system.out.println(root.getValue()+"");
      reversePrint(root.getLeft());
    }
  }
  public static TreeNode maxNode(TreeNode root)
  {
    if(root == null)
      return null;
    while(root.getRight() != null)
      root = root.getRight();
    return root;
  }
}