Java Palindrome checker

Question

I have a issue with my palindrome checker as it is not working properly. It must be able to test these 4 things:

    TestPalindrome("Madam, I'm Adam", true);
    TestPalindrome("addbda", false );
    TestPalindrome("", false);
    TestPalindrome("Dammit, I'm mad", true);

This is my code for the palindrome:

public static boolean IsPalindrome( String inputString )
{
    String reverse = "";
    for(int i = inputString.replaceAll("[^a-zA-Z ]", "").length() -1; i>=0; i--){
        reverse = reverse + inputString.replaceAll("[^a-zA-Z ]", "").charAt(i);
    }
    if(inputString.replaceAll("[^a-zA-Z ]", "").equalsIgnoreCase(reverse.toString()) && !inputString.replaceAll("[^a-zA-Z ]", "").isEmpty()){
        return true;
    }

    if(!inputString.replaceAll("[^a-zA-Z ]", "").equalsIgnoreCase(reverse.toString()) && !inputString.replaceAll("[^a-zA-Z ]", "").isEmpty()){
        return false;
    }

    if(inputString.replaceAll("[^a-zA-Z ]", "").isEmpty()){
        return false;
    }

    else return true;
         }
}

This is what my output is:

TestPalindrome failed: expected true got false
TestPalindrome passed!
TestPalindrome passed!
TestPalindrome failed: expected true got false

Can anyone help me fix this so I get all passes in the list. I understand similar questions have been asked but I´m not asking how to do a palindrome checker but how to fix my specific one. I used those other questions to learn but for some reason my one doesn't work.

You need to debug your program to figure out the "some reason" which is preventing your program from passing the tests you run against it. if you add `System.out.println("'" + inputString + "','" + reverse + "'");` after your `for()` loop finishes, what does it say? — Dan O, Apr 10 '16 at 19:48
Well I first try to reverse my inputString, I then put that if the inputString == the reverse of the inputString then it will return true. I also have it to ignore case and symbols and numbers. That is my strategy, Tyler. — FredTheHomie, Apr 10 '16 at 20:00
I'd follow @DanO's suggestion, but here's one other thing (it won't fix the problem but may help avoid other problems): Don't keep repeating `inputString.replaceAll("[^a-zA-Z ]", "")`. Assign it to a variable and use that. — ajb, Apr 10 '16 at 20:00
OK, I think you need to go one further. Follow my suggestion and assign the result of `replaceAll` to a variable, then follow DanO's suggestion but put that variable in your `println` instead of `inputString`. That will show you exactly which variables you're comparing with `equalsIgnoreCase`. That should make it obvious what the problem is. — ajb, Apr 10 '16 at 20:03
This is one of the lines it printed, it seems the inputString contains symbols but the reverse doesn't. Could this be the reason? — FredTheHomie, Apr 10 '16 at 20:04
It would make it all a lot simpler (and more efficient) if you stopped doing the `replaceAll` call all the time: simply assign a new variable `String inputStringStripped = inputString.replaceAll("[^A-Za-z]", "");`, then use `inputStringStripped` instead of `inputString.replaceAll("[^A-Za-z]", "")`. — Andy Turner, Apr 10 '16 at 20:09

score 1 · Answer 1 · edited Jun 20 '20 at 09:12

1

In order to such algorithm to work you need to consider to clean the punctual symbols like comma, semmicolon, aposthrofs etc (am talking about ';:' etc)

Java has a StringBuilder class and in there is a method to reverse strings

so if you clean the String to check, reverse it and compare it again itself you can see if it a palindrome or not...

Example:

public static void main(String[] args) {
    String word = "Madam, I'm Adam";
    String word2 = "addbda";
    String word3 = "";
    String word4 = "Dammit, I'm mad";
    System.out.println(IsPalindrome(word));
    System.out.println(IsPalindrome(word2));
    System.out.println(IsPalindrome(word3));
    System.out.println(IsPalindrome(word4));
}

private static boolean IsPalindrome(String word) {
    String wordClean = word.replaceAll("[^a-zA-Z  ]", "");
    String reversedWord =  new StringBuilder(wordClean).reverse().toString();
    System.out.println(wordClean);
    System.out.println(reversedWord);
        return reversedWord.equalsIgnoreCase(wordClean)&&!wordClean.isEmpty();
}

this will print

MadamImAdam madAmImadaM true

addbda adbdda false

false (empty check)

DammitImmad dammItimmaD true

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 10 '16 at 20:03

ΦXocę 웃 Пepeúpa ツ

47,427
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Why not just replace everything that's not in `[A-Za-z]` with nothing, rather than just removing specific characters outside that range? – Andy Turner Apr 10 '16 at 20:07
The third one should come out as false, not true. Everything else worked fine. The third one is when the inputString is null or "". What can I do to deal with that? – FredTheHomie Apr 10 '16 at 20:13
@Xoce웃Пepeúpa it's basically what OP does in the question using `[^A-Za-z ]` - it's just that includes space too. – Andy Turner Apr 10 '16 at 20:14
@FredTheHomie thanks, I forgot to check if string is empty, now in there in the return statement... give a try and let me know... – ΦXocę 웃 Пepeúpa ツ Apr 10 '16 at 20:26

score 0 · Answer 2 · answered Apr 10 '16 at 20:11

0

You are not removing spaces, so only strings with spaces in the same places are good. Just use [^a-zA-Z] against [^a-zA-Z ]

answered Apr 10 '16 at 20:11

dey

3,022
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Thank it now works perfectly fine. I appreciate the help from you and everyone. – FredTheHomie Apr 10 '16 at 20:19

Java Palindrome checker

2 Answers2

Example:

Linked