978. Longest Turbulent Subarray

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A subarray is turbulent when the comparison between neighbours keeps flipping: up, down, up, ... or down, up, down, ... (equal neighbours break it). Return the length of the longest turbulent subarray of arr. A single element counts as length 1.

Example

arr = [9,4,2,10,7,8,8,1,9]  ->  5   ([4,2,10,7,8])
arr = [4,8,12,16]           ->  2

Constraints

• 1 <= arr.length <= 4 * 10^4
• 0 <= arr[i] <= 10^9