First Non-Repeating Character

/*
 * Problem : Process one line of text.
 * Input   : One line of text.
 * Output  : The first unique character.
 * Approach: Two passes.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(String s) {
        // Step 1: Count every character. 256 places are enough for ASCII.
        int[] counts = new int[256];
        for (int i = 0; i < s.length(); i++) {
            counts[s.charAt(i)]++;
        }

        // Step 2: Walk through the word again, in the original order.
        for (int i = 0; i < s.length(); i++) {
            // Step 3: The first character with the count 1 is the answer.
            if (counts[s.charAt(i)] == 1) {
                return String.valueOf(s.charAt(i));
            }
        }
        return "none";
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.hasNextLine() ? scanner.nextLine() : "";
        System.out.println(solve(s));
    }
}