Question

How to check if a string is a palindrome ignoring case and non-alphanumeric characters in Java

Answer 1

public class PalindromeChecker {

    public static boolean isPalindrome(String str) {
        StringBuilder filtered = new StringBuilder();

        // Filter out non-alphanumeric characters and convert to lowercase
        for (char ch : str.toCharArray()) {
            if (Character.isLetterOrDigit(ch)) {
                filtered.append(Character.toLowerCase(ch));
            }
        }

        String clean = filtered.toString();
        System.out.println(clean);

        // Check if the filtered string is a palindrome
        int len = clean.length();
        for (int i = 0; i < len / 2; i++) {
            if (clean.charAt(i) != clean.charAt(len - 1 - i)) {
                return false;
            }
        }

        return true;
    }

    public static void main(String[] args) {
        String input = "+^-Ab#c!D 50...#  05*()dcB[]A##@!$";

        if (isPalindrome(input)) {
            System.out.println("The string is a palindrome.");
        } else {
            System.out.println("The string is not a palindrome.");
        }
    }
}


/*
run:
  
abcd5005dcba
The string is a palindrome.
  
*/

 

70+ SQL courses for beginners and professionals

Answer 2

public class PalindromeChecker {

    public static boolean isPalindrome(String str) {
        StringBuilder filtered = new StringBuilder();

        // Filter out non-alphanumeric characters and convert to lowercase
        for (char ch : str.toCharArray()) {
            if (Character.isLetterOrDigit(ch)) {
                filtered.append(Character.toLowerCase(ch));
            }
        }

        String clean = filtered.toString();
        System.out.println(clean);

        // Reverse the filtered string and compare
        String reversed = new StringBuilder(clean).reverse().toString();
        return clean.equals(reversed);
    }

    public static void main(String[] args) {
        String input = "+^-Ab#c!D 50...#  05*()dcB[]A##@!$";

        if (isPalindrome(input)) {
            System.out.println("The string is a palindrome.");
        } else {
            System.out.println("The string is not a palindrome.");
        }
    }
}



/*
run:
  
abcd5005dcba
The string is a palindrome.
  
*/

 

70+ SQL courses for beginners and professionals

Answer 3

public class PalindromeChecker {

    public static boolean isPalindrome(String s) {
        // Remove non-alphanumeric characters and convert to lowercase
        String normalized = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
        System.out.println(normalized);

        // Reverse the string and compare
        String reversed = new StringBuilder(normalized).reverse().toString();
        return normalized.equals(reversed);
    }

    public static void main(String[] args) {
        String s = "+^-Ab#c!D 50...#  05*()dcB[]A##@!$";
        
        System.out.println(isPalindrome(s));
    }
}



/*
run:
  
abcd5005dcba
true
  
*/

 

70+ SQL courses for beginners and professionals