面試題33： 二叉搜索樹的後續遍歷序列

題目：輸入一個整數數組，判斷該數組是不是某二叉搜索樹的後序遍歷的結果。如果是則輸出Yes,否則輸出No。假設輸入的數組的任意兩個數字都互不相同。

class Solution:
    def Binary_search_tree_subsequent_traversal(self, sequence):
        # write code here
        if not sequence or len(sequence) <= 0:
            return False
        root = sequence[-1]
        i = 0

        # 找出左小右大的分界點i,此時i屬於右子樹
        for node in sequence[:-1]:
            if node > root:
                break
            i += 1

        # 如果在右子樹中有比根節點小的值，直接返回False
        for node in sequence[i:-1]:
            if node < root:
                return False

        # 判斷左子樹是否爲二叉搜索樹
        left = True
        if i > 0:
            left = self.Binary_search_tree_subsequent_traversal(sequence[:i])
        # 判斷右子樹是否爲二叉搜索樹
        right = True
        if i < len(sequence)-1:
            right = self.Binary_search_tree_subsequent_traversal(sequence[i:-1])

        return left and right
if __name__=="__main__":
    list = [2,4,3,7,10,9,6]
    solution = Solution()
    a = solution.Binary_search_tree_subsequent_traversal(list)
    print(a)