private void calc(TreeNode node, StringBuilder builder) {
	   builder.append(node.val);
	   
	   if(node.left == null && node.right == null) {
		   sum += Integer.valueOf(builder.toString());
		   
		   return;
	   }else{
		   if(null != node.left){
			   calc(node.left, builder);
			   builder.deleteCharAt(builder.length() - 1);
		   }
		   
		   if(null != node.right){
			   calc(node.right, builder);
			   builder.deleteCharAt(builder.length() - 1);
		   }
	   }
	   
   }