class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root == None:
            return []
        path = []
        stack = []
        node = root
        while len(stack) > 0 or node != None:
            if node != None:
                stack.append(node)
                node = node.left
            else:
                node = stack.pop()
                path.append(node.val)
                node = node.right
        return path