Check for Palindromes returning only true or false

JavaScript
1

Tell us what’s happening:

Your code so far

function palindrome(str) {
  // Good luck!
       t = str.toLowerCase();
       x = t.split("");
       y = x.reverse();
       z = y.join("");
       regExp = z.replace(/[\W_]/gi, "");
       if(regExp === str)
         {
           return true;
         }
       else
         {
           return false;
         }

}

palindrome("eye");```
**Your browser information:**

Your Browser User Agent is: ```Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/60.0.3112.78 Chrome/60.0.3112.78 Safari/537.36```.

**Link to the challenge:**
https://www.freecodecamp.org/challenges/check-for-palindromes
1 Like
3

one of function call requires _eye… and why that one is eliminated in regExp.

I cant understand that yet?

If that underscore is removed , how it will be true. it is not possible though.

5

Hey Rmdawson71,

I can understand that non alphanumeric instruction part,

But what i dont understand is _eye needs to be returned as true, as it is one of the challenge condition.

so when I pass the string “_eye” the replace function will eliminate the _ with regExp characters.

So how come the “_eye” condition will return true? because the underscore is eliminated with regExp

I hope you understand my question

Mean while the my code is running , but i dont feel this is a correct form of code. check and tell me.

function palindrome(str) {
   low = str.toLowerCase();
   regExp = low.replace(/[\W_]/g, "");
   s = regExp.split("");
   r = s.reverse();
   j = r.join("");
   if (regExp == j)
     {return true;}
   else {return false;}
}

palindrome("_eye");
7

Rmdawson71,

Thank you for helping me out :slight_smile:

8

This displays whether the string is a palendrome or not

Click Me!
10 
const numeric = "1234567890";
const alphaLower = "abcdefghijklmnopqrstuvwxyz";
const alphaUpper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
// constant time complexity, O(1),
// since the number of numeric, alphabets are constant
function convertToAlphaNumeric(c){ 
    var indexUpper = alphaUpper.indexOf(c);
    if(indexUpper >=0 )
        return alphaLower(index);

    if(alphaLower.indexOf(c) >=0 )
        return c;

    if(numeric.indexOf(c)>=0)
        return c;

    return '';
}
function palindrome(str) {
 // shallow copied into new memory of length of str 
    var arr = Array.from(str, x=> convertToAlphaNumeric(x) );
   
 // to prevent copying whole array into new memory space
 // for every changes, used 2 pointers and change 
 // the value in existing (original) array, "arr".  
    var j=0; 
    for(var i=0; i<arr.length; i++){
        if(arr[i] != ''){
            arr[j++] = arr[i];
        }
    }
    arr.length=j; // resize array without any consuming extra memory   

    // by using 2 pointers, p1 starts from 0 and moving forward, 
    // p2 starts from the end of the array, moving backward,
    // so that we will need to look up only half length of the array
    var p1 = 0; 
    var p2 = arr.length -1;
    while(p1 < p2){
        if(arr[p1] != arr[p2]) return false;
        p1++;
        p2--;
    }
    return true;
}
palindrome('_eye');