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?

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