Example: First Non-Repeating Character using LinkedHashMap in Java

// First Non-Repeating Character using LinkedHashMap
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Optional;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        String input1 = "swiss";
        String input2 = "teeter";
        String input3 = "aabbcc";
        String input4 = "java";
        String input5 = "";

        System.out.println("Input: \"" + input1 + "\" -> First non-repeating character: " + findFirstNonRepeatingCharLinkedHashMap(input1).orElse(' '));
        System.out.println("Input: \"" + input2 + "\" -> First non-repeating character: " + findFirstNonRepeatingCharLinkedHashMap(input2).orElse(' '));
        System.out.println("Input: \"" + input3 + "\" -> First non-repeating character: " + findFirstNonRepeatingCharLinkedHashMap(input3).orElse(' '));
        System.out.println("Input: \"" + input4 + "\" -> First non-repeating character: " + findFirstNonRepeatingCharLinkedHashMap(input4).orElse(' '));
        System.out.println("Input: \"" + input5 + "\" -> First non-repeating character: " + findFirstNonRepeatingCharLinkedHashMap(input5).orElse(' '));
    }

    public static Optional<Character> findFirstNonRepeatingCharLinkedHashMap(String str) {
        // Step 1: Handle null or empty string
        if (str == null || str.isEmpty()) {
            return Optional.empty();
        }

        // Step 2: Use LinkedHashMap to store character counts and maintain insertion order
        Map<Character, Integer> charCounts = new LinkedHashMap<>();
        for (char c : str.toCharArray()) {
            charCounts.put(c, charCounts.getOrDefault(c, 0) + 1);
        }

        // Step 3: Iterate through the LinkedHashMap to find the first character with a count of 1
        for (Map.Entry<Character, Integer> entry : charCounts.entrySet()) {
            if (entry.getValue() == 1) {
                return Optional.of(entry.getKey());
            }
        }

        // Step 4: If no non-repeating character is found
        return Optional.empty();
    }
}