题解 | #牛妹的面试#

解题思路：
1. 边界条件，长度小于等于2，就返回数组长度
2. 单调递增子序列的长度
3. 反向单调递减子序列长度

class Solution:
    def __get_dp_up(self, numberList):
        """ 获取单调递增的最长子序列（可以不连续） """
        dp_up = [1 for i in range(len(numberList))]
        for i in range(1, len(numberList)):
            for j in range(0, i):
                if numberList[i] > numberList[j]:
                    dp_up[i] = max(dp_up[i], dp_up[j] + 1)
        return dp_up

    def mountainSequence(self , numberList ):
        # write code here

        # 边界条件
        if len(numberList) <= 2:
            return len(numberList)

        # 单调递增，最长序列
        dp_up = self.__get_dp_up(numberList)

        # 单调递减，最长序列
        dp_down = self.__get_dp_up(numberList[::-1])[::-1]

        rnt = dp_up[0] + dp_down[0]
        for i in range(1, len(dp_up)):
            rnt = max(rnt, dp_up[i] + dp_down[i])

        return rnt - 1