JavaScript - Find if string is a palindrome - Check for punctuation

Question

I am trying to solve an exercise but the code shows errors. Here are the conditions given for the exercise:

Return true if the given string is a palindrome. Otherwise, return false.

You'll need to remove punctuation and turn everything lower case in order to check for palindromes.

We'll pass strings with varying formats, such as "racecar", "RaceCar", and "race CAR" among others.

My attempt:

function palindrome(str) {
    str = str.toLowerCase();
    str = str.replace(",", "");
    str = str.replace(".", "");
    str = str.replace(":", "");
    str = str.replace(";", "");
    str = str.replace("-", "");
    str = str.replace(",", "");
    str = str.replace(" ", "");
    for (var i = 0; i <= (str.length / 2); i++) {
        if (str[i] != str.length - i) return false;
    }
    return true;
}

So we need to guess errors or complete this exercise for you? — zerkms, Sep 14 '15 at 07:31
`str[i] != str.length-i` --- what this comparison is about? You're comparing a letter with... a number? — zerkms, Sep 14 '15 at 07:31
possible duplicate of [Palindrome check in Javascript](http://stackoverflow.com/questions/14813369/palindrome-check-in-javascript) — Hanky Panky, Sep 14 '15 at 07:32
@Hanky웃Panky: Not quite, this one has a bit of leniency for punctuation. — Cerbrus, Sep 14 '15 at 07:49

Cerbrus · Accepted Answer · 2015-09-14T07:46:52.573

6

You were quite close.
Replace:

if (str[i] != str.length-i)

With:

if (str[i] != str[str.length - (i + 1)])

The last character of the string is at str.length - (i + 1), and you forgot to get the actual character. Instead, you were comparing it with the index of that character.

Now, you could shorten the function a lot:

function checkPalindrome(str) {
    // remove punctuation, to lower case.
    str = str.replace(/[.,?:;\/() _-]/g, '').toLowerCase();
    // Compare the string with it's reversed version.
    return str == str.split('').reverse().join('');
}

edited Sep 14 '15 at 07:46

answered Sep 14 '15 at 07:31

Cerbrus

70,800
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will `/[^a-z0-9]/g` be better to remove all non-alphanumeric characters? – Tushar Sep 14 '15 at 07:36
+one Removed my Duplicate – Tushar Sep 14 '15 at 07:37
@Tushar: `checkPalindrom("rácecér")` will return `true`, for that regex. – Cerbrus Sep 14 '15 at 07:37
I followed this code. Now I am getting the following error, `assert.strictEqual(palindrome("0_0 (: /-\ :) 0-0"), true, "\"0_0 (: /-\\ :) 0-0\" is a palindrome");"0_0 (: /-\ :) 0-0" is a palindrome: expected false to equal true` – Sep 14 '15 at 07:45
@FahadUddin: In that case, you need to trim some more punctuation. I edited my answer. – Cerbrus Sep 14 '15 at 07:49
Another way - `var y = x.match(/[a-zA-Z]*/g).join("").toLowerCase();` – AdityaParab Sep 14 '15 at 08:00
@AdityaParab: Nope. That will ignore stuff like `éíô` etc. – Cerbrus Sep 14 '15 at 08:08
Thank you for the info, mate. How do we catch those characters? – AdityaParab Sep 14 '15 at 08:11
By only removing characters we don't want, instead of trying to get everything you _do_ want to match. – Cerbrus Sep 14 '15 at 08:13

score 2 · Answer 2 · answered Jun 14 '19 at 14:50

2

My solution for the problem:

function palindrome(str) {
    return str.toLowerCase() == str.toLowerCase().split('').reverse().join('');
}

In terms of performance this solution is faster than using a for loop or regular expression

answered Jun 14 '19 at 14:50

P.Dederer

62
3

score -3 · Answer 3 · answered Sep 14 '15 at 07:36

-3

This is quite simple. just make and call below function:

var isPalindrome = function(str){ return str == str.split('').reverse().join(''); }

answered Sep 14 '15 at 07:36

Muhammad Arslan Sajid

16
4

score -4 · Answer 4 · edited May 23 '17 at 11:51

-4

function palindrome(str) {
    var len = str.length;
    for ( var i = 0; i < Math.floor(len/2); i++ ) {
        if (str[i] !== str[len - 1 - i]) {
            return false;
        }
    }
    return true;
}

Optimized version

Source : See here

edited May 23 '17 at 11:51

Community

1
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answered Sep 14 '15 at 07:33

Pirate X

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It's a placebo optimisation. – zerkms Sep 14 '15 at 07:33
It would still be beneficial. (Not considering extremely large palindromes) – Pirate X Sep 14 '15 at 07:36
Eh, no. This completely ignores the question's requirement for the check to be case insensitive and to remove punctuation. – Cerbrus Sep 14 '15 at 07:51

JavaScript - Find if string is a palindrome - Check for punctuation

4 Answers4