<p>A phrase is a <strong>palindrome</strong> if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.</p>

<p>Given a string <code>s</code>, return <code>true</code><em> if it is a <strong>palindrome</strong>, or </em><code>false</code><em> otherwise</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;A man, a plan, a canal: Panama&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> &quot;amanaplanacanalpanama&quot; is a palindrome.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;race a car&quot;
<strong>Output:</strong> false
<strong>Explanation:</strong> &quot;raceacar&quot; is not a palindrome.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot; &quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> s is an empty string &quot;&quot; after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 2 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists only of printable ASCII characters.</li>
</ul>

from curses.ascii import isalnum


class Solution:
    def isPalindrome(self, s: str) -> bool:
        ch_arr = [ch for ch in s if isalnum(ch)]
        size = len(ch_arr)
        if size < 2 : 
            return True
        stack = []
        push_idx = size//2 - 1
        pop_idx = push_idx + 1
        if size % 2 == 1:
            pop_idx += 1
        for i in range(push_idx+1):
            l = ch_arr[i].lower()
            stack.append(l)
        for i in range(pop_idx, size+1):
            if stack and stack.pop() != ch_arr[i].lower():
                return False
        return True


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