Palindrome and Flutter Stuff

palindromeexample.dart

void main() {
  
  print('Should all be true:');
  print(Palindrome.check('radar'));
  print(Palindrome.check('noon'));
  print(Palindrome.check(''));
  print(Palindrome.check('123321'));
  print(Palindrome.check('12,32,1'));
  print(Palindrome.check('1 2 3 2 1'));
  print(Palindrome.check('1  2 3 2 1'));
  print(Palindrome.check('Rise to vote, sir!'));
  print(Palindrome.check('aA'));
  print(Palindrome.check('?aA'));
  print(Palindrome.check(',aA'));
  print(Palindrome.check(':aA'));
  print('');
  
  print('Should all be false:');
  print(Palindrome.check('radarx'));
  print(Palindrome.check('ABC'));
  print(Palindrome.check('?ABC'));
  print(Palindrome.check('...ABC'));
 
     
}

// lambda to mimic Java's Character.isLetterOrDigit()
bool isLetterOrDigit(String s, int idx) => s[idx].contains(RegExp(r'[\da-zA-Z]'));


class Palindrome {
  
  static bool check(String s) {
    
    // noon radar radarx 
    // 0123 01234 012345
    
    // modify the string, such that spces and punctuation are removed
   
    int mid = s.length ~/ 2;
    int start = 0;
    int end = s.length - 1;
    
    while (start < mid) {
        while (!isLetterOrDigit(s, start)) start++;
        while (!isLetterOrDigit(s,end))end--;
       
        if (s[start].toLowerCase() != s[end].toLowerCase()) 
          return false;
      start++;
      end--;
    }
    return true;
  }
  
}

bool checkPalindrome(String inputString) {
    for (int i = 0; i < inputString.length ~/ 2; i++) {
    if (inputString[i] != inputString[inputString.length - i - 1]) return false;
  }
  return true;
    }