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# 0845. Longest Mountain in Array

<https://leetcode.com/problems/longest-mountain-in-array>

## Description

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?

## ac

```java
```