How to remove all non-alphabet characters, javascript

Question

I am asked to check if a string is a Palindrome. To not be case sensitive. To ignore all characters that are not letters.

My Answer

 function palindrome(str) {
  var oldStr = str.toLowerCase().replace(/\s+|\,|\.|\_|\-|\:|\(|\)|\/|\\/g,  '');

  var newStr = str.replace(/\s+|\,|\.|\_|\-|\:|\(|\)|\/|\\/g, '').split("").reverse().join("").toLowerCase();

  if ( oldStr === newStr){
    return true;
  }
  else {
    return false;
  }
}
palindrome("ininiNI");

The function is to be checked with any string possibility. Example: ("0_0 (: /-\ :) 0-0") Which according to the requirements should return true.

I could not find a better solution in JavaScript then the one above.

Is there a faster/better way than just writing out each possible character to be removed/replaced? (especially since what I wrote is far from exhaustive...)

Wrong duplicate linked, link has an Java solution. Here a JS solution I searched: https://stackoverflow.com/questions/9364400/remove-not-alphanumeric-characters-from-string-having-trouble-with-the-char — Doomenik, Sep 18 '17 at 09:47
The regex \W takes away most of the options but not all. palindrome("_eye") still does not return True. Neither does the String example I gave above. — Chuck, Sep 18 '17 at 09:50
@Doomenik Ah ok thanks, that answer sums it up. I need to also add \_ to take out underscores. — Chuck, Sep 18 '17 at 09:56
Just tried it, works great. Where could I find an explanation for what exactly [^A-Za-z0-9] means/does...? — Chuck, Sep 18 '17 at 09:58
@Doomenik actually the `.lowerCase()` call is useless here, it can be ommitted with `/[^a-z]/ig`, the `i` flag will treat both uppercase and lowercase. — cнŝdk, Sep 18 '17 at 10:02
@Doomenik It may look a little bit harder to understand, but it's worth of use and very powerful whne you use it ;) — cнŝdk, Sep 18 '17 at 10:05
@Chuck This is the [`/[^a-z0-9]/ig`](https://regex101.com/r/8Ud55q/1) you will need to use, you can find [all explanations **here**](https://regex101.com/r/8Ud55q/1). — cнŝdk, Sep 18 '17 at 10:11
@chsdk I tried ' /[^a-z0-9]/ig ', taking out ' .lowerCase()' . It didn't return true for palindrome("A man, a plan, a canal. Panama") — Chuck, Sep 18 '17 at 10:15
Yes because the regex is used to replace all the non alphanumeric charcters, so after calling it `A` won't be chnaged to `a`. — cнŝdk, Sep 18 '17 at 10:19

ElChupacabra · Accepted Answer · 2017-09-18T10:00:48.917

There is no need to call toLowerCase() and replace() twice. You can also cut string in a half, reverse one part and then compare. That way you can speed up your function few times at least.

Optimized function may look like that:

function palindrome(str) {
  str = str.toLowerCase().replace(/[^a-z]/g, '');
  var max = str.length - 1;
  for (var i = Math.floor(max / 2); i >= 0; i--) {
    if (str[i] != str[max - i]) {
      return false;
    }
  }
  return true;
}

palindrome("inabcbani"); //true
palindrome("abcddcba"); //true
palindrome("a*#$(b)&^@%@%(*a"); //true
palindrome("abba"); //true
palindrome("abcdba"); //false

For loop will be the fastest way in my opinion as it's quick and simple. You can return false once you find first character that doesn't match.

Could you show an example of what you mean please. – Chuck Sep 18 '17 at 09:59 — Chuck, Sep 18 '17 at 09:59

How to remove all non-alphabet characters, javascript

1 Answers1