Check Palindrome with Loop

Summary

Determine whether a string is a palindrome using explicit loops and ignoring non-alphanumeric characters.

Problem statement

Write is_palindrome(s) that returns True if the string s is a palindrome when considering only alphanumeric characters and ignoring case, otherwise return False. Use loops (for or while) to compare characters; do not use slicing like s[::-1] or the reversed() built-in for the main comparison logic. Examples of treatment: - 'A man, a plan, a canal: Panama' -> True - 'race a car' -> False - Empty string or strings with no alphanumeric characters are palindromes (return True).

Task

Implement a function that checks if a string reads the same forwards and backwards, ignoring case and non-alphanumeric characters, using loops (no slicing for reversal).

Examples

Input format

A single argument: s (string).

Output format

Boolean True if palindrome according to the rules, otherwise False.

Constraints

String length <= 1000. Use explicit loops for comparison; you may use str.isalnum() and str.lower().

Samples