Example: FindFirstNonRepeatingStreamDirect in Java

// FindFirstNonRepeatingStreamDirect
import java.util.Optional;

public class Main {
    public static Optional<Character> findFirstNonRepeatingStreamDirect(String s) {
        if (s == null || s.isEmpty()) {
            return Optional.empty();
        }

        // Step 1: Stream characters of the string
        return s.chars()
            .mapToObj(c -> (char) c) // Convert int stream to Character stream
            .filter(c -> s.indexOf(c) == s.lastIndexOf(c)) // Filter for non-repeating characters
            .findFirst(); // Get the first one
    }

    public static void main(String[] args) {
        System.out.println("\n--- Stream API with Direct Index Check Approach ---");
        System.out.println("stress -> " + findFirstNonRepeatingStreamDirect("stress").orElse(null)); // t
        System.out.println("aabbc -> " + findFirstNonRepeatingStreamDirect("aabbc").orElse(null));   // c
        System.out.println("aabb -> " + findFirstNonRepeatingStreamDirect("aabb").orElse(null));     // null
        System.out.println("java -> " + findFirstNonRepeatingStreamDirect("java").orElse(null));     // j
        System.out.println(" -> " + findFirstNonRepeatingStreamDirect("").orElse(null));           // null
        System.out.println("zzzaac -> " + findFirstNonRepeatingStreamDirect("zzzaac").orElse(null)); // c
    }
}