text: # https://leetcode.com/problems/binary-tree-inorder-traversal
  
  # Definition for a binary tree node.
  # class TreeNode:
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  
  class Solution:
      def inorderTraversal(self, root):
          self.ans = []
  
          def helper(node):
              if not node:
                  return
              helper(node.left)
              self.ans.append(node.val)
              helper(node.right)
  
          helper(root)
          return self.ans
  