Valid Mountain Array
<p>Given an array of integers <code>arr</code>, return <em><code>true</code> if and only if it is a valid mountain array</em>.</p>

<p>Recall that arr is a mountain array if and only if:</p>

<ul>
	<li><code>arr.length &gt;= 3</code></li>
	<li>There exists some <code>i</code> with <code>0 &lt; i &lt; arr.length - 1</code> such that:
	<ul>
		<li><code>arr[0] &lt; arr[1] &lt; ... &lt; arr[i - 1] &lt; arr[i] </code></li>
		<li><code>arr[i] &gt; arr[i + 1] &gt; ... &gt; arr[arr.length - 1]</code></li>
	</ul>
	</li>
</ul>
<img src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0900-0999/0941.Valid%20Mountain%20Array/images/hint_valid_mountain_array.png" width="500" />
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> arr = [2,1]
<strong>Output:</strong> false
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> arr = [3,5,5]
<strong>Output:</strong> false
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> arr = [0,3,2,1]
<strong>Output:</strong> true
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= arr.length &lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= arr[i] &lt;= 10<sup>4</sup></code></li>
</ul>
Array
class Solution {
    public boolean validMountainArray(int[] arr) {
        int n = arr.length;
        if (n < 3) {
            return false;
        }
        int i = 0, j = n - 1;
        while (i + 1 < n - 1 && arr[i] < arr[i + 1]) {
            ++i;
        }
        while (j - 1 > 0 && arr[j - 1] > arr[j]) {
            --j;
        }
        return i == j;
    }
}