Longest Mountain in Array

You may recall that an array arr is a mountain array if and only if:

• arr.length >= 3
• There exists some index i with 0 < i < arr.length - 1 such that:
• arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
• arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr, return the length of the longest subarray, which is a mountain. Return 0 if there is no mountain subarray.

No mountain — there must be strictly increasing then strictly decreasing sides of length >= 1 each.