Example: Anagram Checker (Frequency Array) in Java

// Anagram Checker (Frequency Array)
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {

    /**
     * Checks if two strings are anagrams using a frequency array.
     * Ignores case and non-alphabetic characters.
     * Assumes ASCII characters for array size.
     *
     * @param str1 The first string.
     * @param str2 The second string.
     * @return true if the strings are anagrams, false otherwise.
     */
    public static boolean areAnagramsUsingFrequencyArray(String str1, String str2) {
        // Step 1: Handle null or empty strings
        if (str1 == null || str2 == null) {
            return false;
        }
        if (str1.isEmpty() && str2.isEmpty()) {
            return true;
        }

        // Step 2: Normalize strings (remove spaces, convert to lowercase)
        String processedStr1 = str1.replaceAll("\\s", "").toLowerCase();
        String processedStr2 = str2.replaceAll("\\s", "").toLowerCase();

        // Step 3: Check if lengths are different after processing
        if (processedStr1.length() != processedStr2.length()) {
            return false;
        }

        // Step 4: Create a frequency array for characters (assuming ASCII)
        // Size 256 for all possible ASCII character values
        int[] charCounts = new int[256];

        // Step 5: Iterate through the first string and increment character counts
        for (char c : processedStr1.toCharArray()) {
            charCounts[c]++;
        }

        // Step 6: Iterate through the second string and decrement character counts
        for (char c : processedStr2.toCharArray()) {
            charCounts[c]--;
        }

        // Step 7: Check if all character counts are zero
        // If they are, it means all characters matched in frequency
        for (int count : charCounts) {
            if (count != 0) {
                return false; // Mismatch found
            }
        }

        // All counts are zero, so they are anagrams
        return true;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("--- Anagram Checker (Frequency Array Method) ---");
        System.out.print("Enter first string: ");
        String s1 = scanner.nextLine();

        System.out.print("Enter second string: ");
        String s2 = scanner.nextLine();

        boolean isAnagram = areAnagramsUsingFrequencyArray(s1, s2);

        if (isAnagram) {
            System.out.println("\"" + s1 + "\" and \"" + s2 + "\" are anagrams.");
        } else {
            System.out.println("\"" + s1 + "\" and \"" + s2 + "\" are NOT anagrams.");
        }

        scanner.close();
    }
}