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beginner
Write a function that checks if a single word is a palindrome. DO NOT worry about spaces, punctuation, mixed capitalization, or unicode characters. Assume simple lowercase alphabetic strings only.
intermediate
Write a function that checks if a given phrase is a palindrome. It must ignore spaces and be case-insensitive. Do not worry about complex unicode.
expert
Write a function that checks if a string is a palindrome. It must ignore spaces, punctuation, and correctly handle complex unicode/Latin characters. Optimize it to run in O(n) time with O(1) extra space.