def lrm_f(self,root):
        stack=[]
        result_stack=[]
        if root is not None:
            stack.append(root)
            while len(stack)!=0:
                root=stack.pop()
                result_stack.append(root)
                if root.left is not None:
                    stack.append(root.left)
                if root.right is not None:
                    stack.append(root.right)
            while len(result_stack)!=0:
                result3.append(result_stack.pop().val)