Misbehavior

class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        cur = root  #借助临时的cur，不要修改root
        res = []
        stack = []
        while cur or stack:
            if cur:  # 一直往左走，全部入栈
                stack.append(cur) 
                cur = cur.left
            else:  # 取出栈顶节点，处理，再处理该节点的右子树   
                cur = stack.pop()
                res.append(cur.val)  
                cur = cur.right
        return res

class Solution:
    def preorderTraversal(self, root: TreeNode) -> List[int]:
        cur = root
        res = []
        stack = []
        while cur or stack:
            if cur:
                stack.append(cur)  # 每一个节点都放入栈中
                res.append(cur.val)
                cur = cur.left
            else:
                cur = stack.pop()  # 这里pop出来的是已经访问过的节点
                cur = cur.right  # 还需要指向右子树
        return res