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Java-based LeetCode algorithm problem solutions, regularly updated

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941\. Valid Mountain Array

Easy

Given an array of integers `arr`, return _`true` if and only if it is a valid mountain array_.

Recall that arr is a mountain array if and only if:

*   `arr.length >= 3`
*   There exists some `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]`

![](https://assets.leetcode.com/uploads/2019/10/20/hint_valid_mountain_array.png)

**Example 1:**

**Input:** arr = [2,1]

**Output:** false

**Example 2:**

**Input:** arr = [3,5,5]

**Output:** false

**Example 3:**

**Input:** arr = [0,3,2,1]

**Output:** true

**Constraints:**

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