text: from collections import deque
  # Definition for a binary tree node.
  # class TreeNode:
  #     def __init__(self, val=0, left=None, right=None):
  #         self.val = val
  #         self.left = left
  #         self.right = right
  class Solution:
      def inorderTraversal(self, root: TreeNode) -> List[int]:
          if not root:
              return root
          res=[]
          stack=[]
          while stack or root:
              if root:
                  stack.append(root)
                  root = root.left 
              else:
                  node=stack.pop()
                  res.append(node.val)
                
                  root=node.right
          return res        