Longest Turbulent Subarray

A subarray A[i], A[i+1], ..., A[j] of A is said to be turbulent if and only if:

• For i <= k < j, A[k] > A[k+1] when k is odd, and A[k] < A[k+1] when k is even;

• OR, for i <= k < j, A[k] > A[k+1] when k is even, and A[k] < A[k+1] when k is odd.

That is, the subarray is turbulent if the comparison sign flips between each adjacent pair of elements in the subarray.

Return the length of a maximum size turbulent subarray of A.

Example 1:

Input: [9,4,2,10,7,8,8,1,9]
Output: 5
Explanation: (A[1] > A[2] < A[3] > A[4] < A[5])

Example 2:

Input: [4,8,12,16]
Output: 2

Example 3:

Input: [100]
Output: 1

Note:

1. 1 <= A.length <= 40000

2. 0 <= A[i] <= 10^9

分析：

若弯曲则up由down来，down由up来，这样其实一直保存了最大曲线的长度且递增，同时也保存了当前现状。

loop里每次res也更新得到最大。

class Solution:
    def maxTurbulenceSize(self, A: List[int]) -> int:
        n = len(A)
        up,down,res=1,1,1
        for i in range(1,n):
            if A[i] > A[i-1]:
                up = down+1
                down =1
            elif A[i] < A[i-1]:
                down = up+1
                up = 1
            else:
                up=down=1
            res = max(res,up,down)
        return res