Palindrome issue with JavaScript

Question

I need to write a code with a function that has a parameter str that evaluates if the word is a palindrome or not, it should return true, else ir should return false.

Note: I need to remove all non-alphanumeric characters.

I wrote the code below but it is giving the opposite of the result expected:

It is giving false for all the cases.
Not able to remove the underscore.
and when use console.log below the image I get.

Code:

function palindrome(str) {
  var exc = /[^\w_]/gi;
  var repStr = str.toLowerCase().replace(exc, "");
  console.log("Replaced string id: " + repStr);
  len = repStr.length -1

  for (var i = 0; i <= len; i++) {
    if (str[i] !== repStr[len] - i) {
      return false;
    }
  }
  return true;
}

console.log(palindrome("eye"));
console.log(palindrome("_eye"));
console.log(palindrome("race car"));
console.log(palindrome("not a palindrome"));
console.log(palindrome("A man, a plan, a canal. Panama"));
console.log(palindrome("never odd or even"));
console.log(palindrome("nope"));
console.log(palindrome("almostomla"));
console.log(palindrome("My age is 0, 0 si ega ym"));
console.log(palindrome("1 eye for of 1 eye."));
console.log(palindrome("0_0 (: /-\ :) 0-0"));
console.log(palindrome("five|\_/|four"));

Underscore is a part of alphanumeric, your regex won't remove them. — nitte93
– nitte93, Commented Jan 21, 2018 at 15:40

Stefan Octavian · Accepted Answer · 2018-01-21 16:57:28Z

1

There are 2 mistakes in your code. 1) the RegExp is not replacing the underscore as [^\w_] reads as "everything that is not a word character OR an underscore". Try

/[\W_]/g

which reads as "one of the following: any character that is not a word character, underscores"

OR

/[^0-9a-z]/g

which reads as "anything that is not: digits (from 0 to 9), english alphabet letters".

2) For it to work you need to write

if(repStr[i] !== repStr[len - i])

instead of

if(str[i] !== repStr[len] - i)

edited Jan 21, 2018 at 16:57

answered Jan 21, 2018 at 15:36

Stefan Octavian

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4 Comments

Hacene .N Over a year ago

Thanks a lot for the help!!

nitte93 Over a year ago

/[0-9a-z_]/ also trims the first char, isn't it? 'eye'.replace(/[0-9a-z_]/, '') give ye

Stefan Octavian Over a year ago

I meant /[^0-9a-z]/g. I'm sorry. I'm dizzy

Stefan Octavian Over a year ago

Also, that was trimming the first character because it was matching the characters I wanted to keep instead of the other ones and it wasn't global (it didn't have the g flag) so it removed only the first character found

Aswin Ramesh · Accepted Answer · 2018-01-21 15:50:42Z

you can simply replace the two of your lines

for (var i = 0; i <= len; i++, len--) {
    if (str[i] !== repStr[len]) {

check this

function palindrome(str) {
  var exc = /[^\w_]/gi;
  var repStr = str.toLowerCase().replace(exc, "");
  console.log("Replaced string id: " + repStr);
  len = repStr.length -1

  for (var i = 0; i <= len; i++, len--) {
    if (str[i] !== repStr[len]) {
      return false;
    }
  }
  return true;
}

console.log(palindrome("eye"));
console.log(palindrome("_eye"));
console.log(palindrome("race car"));
console.log(palindrome("not a palindrome"));
console.log(palindrome("A man, a plan, a canal. Panama"));
console.log(palindrome("never odd or even"));
console.log(palindrome("nope"));
console.log(palindrome("almostomla"));
console.log(palindrome("My age is 0, 0 si ega ym"));
console.log(palindrome("1 eye for of 1 eye."));
console.log(palindrome("0_0 (: /-\ :) 0-0"));
console.log(palindrome("five|\_/|four"));

Carloluis · Accepted Answer · 2018-01-21 16:17:27Z

0

Try this out:

function palindrome(str) {
    const letters = str.replace(/[^a-z]/gi, ''); // replace any char that is not in the set [a-z] range
    const lowercase = letters.toLowerCase();
    const reversed = lowercase.split('').reverse().join('');
    return lowercase === reversed;
}

answered Jan 21, 2018 at 16:17

Carloluis

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