DSA: Character Classification for Palindromes

Palindrome problems commonly compare only letters and numbers. Treat every other character, including spaces, punctuation, and symbols, as ignorable.

func isAlphanumeric(_ character: Character) -> Bool {
    character.isLetter || character.isNumber
}

func shouldIgnoreForPalindrome(_ character: Character) -> Bool {
    !isAlphanumeric(character)
}

isAlphanumeric("A")               // true
isAlphanumeric("7")               // true
shouldIgnoreForPalindrome(" ")    // true
shouldIgnoreForPalindrome("!")    // true

Use the helpers while moving two pointers inward. Skip ignored characters before comparing the remaining characters, usually after normalizing their case.

Swift’s Character.isLetter and Character.isNumber properties are Unicode-aware, so this works beyond ASCII letters and digits.