<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://assets.leetcode.com/uploads/2019/10/20/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>

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        
        # early return in case of an empty array
        if arr is None:
            return False
        
        length = len(arr)
        
        # this is by the rules of the issue
        if length < 3:
            return False
        
        is_climbing = True        
        highest_index = -1
        
        index = 1
        while index < length:
            previous = arr[index - 1]
            current = arr[index]
            
            # expecting either strict raising or strict decreasing
            if previous == current:
                return False
            
            if is_climbing:
                
                # expected previous to be below current
                if previous < current:
                    pass
                else:
                    # must have reached the top of the mountain 
                    # and expect or consequent elements to be lower
                    is_climbing = False
                    # print(f"getting into the mountain top {previous=} {current=} {index=}")
                    highest_index = index - 1
                
            else:
                
                # in case when we are decreasing we expect current value to be lower than the previous one
                if previous > current:
                    pass
                else:
                    # otherwise its not a mountain
                    return False     
            
            index += 1
        
        # all conditions passed
        # need to make sure that there were at least one increasing and one decreasing element
        
        # print(f"{highest_index=}")
        return highest_index > 0 and highest_index < length
        
        
        
18000