Arrays & Hashing
Palindrome checker
Task:
- Write a function that determines whether a given string is a palindrome.
Rules:
- A palindrome is a word, phrase, number, or other sequence of characters that reads the same backward as forward.
- Ignore case sensitivity (e.g., “Racecar” is considered a palindrome).
- Remove non-alphanumeric characters before checking (e.g., “A man, a plan, a canal, Panama!” is a palindrome).
Example:
Input: “TAS AT”
Output: true
Input: “1234 a 4323”
Output: false
Input: “Arazi küçük. İz ara”
Output: true
public class PalindromeChecker {
public static boolean isPalindrome(String input) {
// Normalize the string: convert to lowercase and remove non-alphanumeric characters
StringBuilder normalized = new StringBuilder();
for (char ch : input.toCharArray()) {
// Check if the character is alphanumeric
if (Character.isLetterOrDigit(ch)) {
normalized.append(Character.toLowerCase(ch));
}
}
// Compare the normalized string with its reverse without using built-in reverse
int left = 0;
int right = normalized.length() - 1;
while (left < right) {
if (normalized.charAt(left) != normalized.charAt(right)) {
return false; // Not a palindrome
}
left++;
right--;
}
return true; // Is a palindrome
}
public static void main(String[] args) {
// Test cases
System.out.println(isPalindrome("TAS AT")); // Output: true
System.out.println(isPalindrome("1234 a 4323")); // Output: false
System.out.println(isPalindrome("Arazi küçük. İz ara")); // Output: true
System.out.println(isPalindrome("A man, a plan, a canal, Panama!")); // Output: true
}
}
import java.util.regex.Pattern;
public class PalindromeChecker {
public static boolean isPalindrome(String str) {
// Convert to lowercase and remove non-alphanumeric characters
String cleanedStr = str.toLowerCase().replaceAll("[^a-zA-Z0-9]", "");
// Check if the cleaned string is equal to its reverse
return cleanedStr.equals(new StringBuilder(cleanedStr).reverse().toString());
}
public static void main(String[] args) {
String str1 = "TAS AT";
String str2 = "1234 a 4323";
String str3 = "Arazi küçük. İz ara";
System.out.println(isPalindrome(str1)); // Output: true
System.out.println(isPalindrome(str2)); // Output: false
System.out.println(isPalindrome(str3)); // Output: true
}
}
