978. Longest Turbulent Subarray

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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

思路：two pointer

class Solution:
    def maxTurbulenceSize(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        res = 0
        help = []
        for i in A:
            if len(help)<2:
                help.append(i)
                continue
            if (i>help[-1] and help[-1]<help[-2]) or (i<help[-1] and help[-1]>help[-2]):
                help.append(i)
            else:
                res = max(res, len(help))
                help = help[-1:] if help[-1]!=i else []
                help.append(i)
        res = max(res, len(help))
        return res
    
                
            

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