JAVA算法练习题day34

43.验证二叉搜索树

要知道二叉搜索树的中序遍历结果是升序序列

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):def isValidBST(self, root):""":type root: Optional[TreeNode]:rtype: bool"""if root is None:return Trueif root.left is None and root.right is None:return Truenums = []def dfs(root):if root is None:returndfs(root.left)nums.append(root.val)dfs(root.right)dfs(root)#写一个判断数组是否为升序数组的函数def isST(nums):for i in range(len(nums)-1):if nums[i]>=nums[i+1]:return Falsereturn Truereturn isST(nums)