python leetcode 98. Validate Binary Search Tree

中序遍历是否为递增数组

class Solution(object):
    def isValidBST(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        #中序遍历为递增数组 
        list = []
        def inorder(root):
            if root == None:
                return 
            inorder(root.left)
            list.append(root.val)
            inorder(root.right)
        
        inorder(root)
        for i in range(len(list)-1):
            if list[i]>=list[i+1]:
                return False
        return True