palindrome.swift

import UIKit

extension String {
    func isAlphanumeric() -> Bool {
        return self.rangeOfCharacter(from: CharacterSet.alphanumerics.inverted) == nil && self != ""
    }
    
    func isAlphanumeric(ignoreDiacritics: Bool = false) -> Bool {
        if ignoreDiacritics { return self.range(of: "[^a-zA-Z0-9]", options: .regularExpression) == nil && self != "" }
        else { return self.isAlphanumeric() }
    }
}

func isPalindrome(string: String) -> Bool {
    var newString = string
    for char in string {
        if !"\(char)".isAlphanumeric() { continue }
        
        while newString.count > 0 {
            guard let lastChar = newString.last else { break }
            newString = String(newString.dropLast())
            
            if char.lowercased() == lastChar.lowercased() { break }
            if "\(lastChar)".isAlphanumeric() { return false }
        }
    }
    
    return true
}

isPalindrome(string: "level") == true ? print("passed") : print("failed")
isPalindrome(string: "algorithm") == false ? print("passed") : print("failed")
isPalindrome(string: "A man, a plan, a canal: Panama.") == true ? print("passed") : print("failed")