题解 | #判断是不是二叉搜索树#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
#
# @param root TreeNode类
# @return bool布尔型
#
class Solution:
    def isValidBST(self, root: TreeNode) -> bool:
        traversed = []
 
        def inordercheck(node):
            if node.left:
                inordercheck(node.left)
            traversed.append(node.val)
            if node.right:
                inordercheck(node.right)
        
        inordercheck(root)
        
        for i in range(len(traversed)):
            if i > 0 and traversed[i] < traversed[i-1]:
                return False
        return True