非递归中序遍历

class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        ans=[]
        stack=[]
        node=root
        while node or stack:
            while node:
                stack.append(node)
                node=node.left
            node=stack.pop()
            ans.append(node.val)
            node=node.right
        return ans