从根节点开始递归 | #二叉搜索树的后序遍历序列#

#
# 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 sequence int整型一维数组 
# @return bool布尔型
#
class Solution:
    def VerifySquenceOfBST(self , sequence: list[int]) -> bool:
        # write code here
        if not sequence:
            return False
        else:
            return self._verify_rec(sequence)
    
    def _verify_rec(self , sequence: list[int]):
        # print(sequence)
        if len(sequence) == 0:
            return True
        elif len(sequence) == 1:
            return True
        else:
            root_node = sequence[-1]
            sequence = sequence[:-1]
            into_right = 0
            left_bound = 0
            for i in range(len(sequence)):
                if sequence[i] == root_node:
                    return False
                elif (not into_right) and sequence[i] > root_node:
                    into_right = 1
                    left_bound = i+0
                elif into_right and sequence[i] < root_node:
                    return False
            if not into_right:
                left_bound = len(sequence)-1
            return self._verify_rec(sequence[:left_bound]) and self._verify_rec(sequence[left_bound:])