https://leetcode.com/problems/longest-mountain-in-array/description/
找最長的山脈
思路：一次遍歷，找山頂（比兩端都高）。若找到，從山頂向兩端發散，求山脈長度，每次更新最大長度。

class Solution:
    def longestMountain(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        n = len(A)
        maxL = 0
        for i in
 
 range(n):
            length = 0  #山脈長度
            #找到山頂
            if i-1 >= 0 and i+1 < n and A[i] > A[i-1] and A[i] > A[i+1]:
                length += 1
                left = right = i  #山頂左右兩側指標
                while left-1 >= 0 and A[left] > A[left-1]:
                    left -= 1
 

                    length += 1
                while right+1 < n and A[right] > A[right+1]:
                    right += 1
                    length += 1
            maxL = max(length, maxL)
        return maxL