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

* `arr.length >= 3`
* There exists some index `i` (0-indexed) 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.

Example 1:
    
    Input: arr = [2,1,4,7,3,2,5] Output: 5 Explanation: The largest mountain is [1,4,7,3,2] which has length 5. 

Example 2:
    
    Input: arr = [2,2,2] Output: 0 Explanation: There is no mountain. 

Constraints:

* `1 <= arr.length <= 104`
* `0 <= arr[i] <= 104`

Follow up:

* Can you solve it using only one pass?
* Can you solve it in `O(1)` space?