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 __init__(self) -> None:
        self.arr = []
    def LDR(self , this: TreeNode):
        if this:
            self.LDR(this.left)
            self.arr.append(this.val)
            self.LDR(this.right)
    def isValidBST(self , root: TreeNode) -> bool:
        # write code here
        self.LDR(root)
        arrsort = self.arr.copy()
        arrsort.sort()
        if self.arr == arrsort:
            return True
        else:
            return False