Intersection of Two Arrays

/*
 * Problem : Common values.
 * Input   : Two arrays.
 * Output  : The sorted common values.
 * Approach: Use a set.
 * Time    : O(n + m + k log k)
 * Space   : O(n + m)
 * 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(int[] a, int[] b) {
        // Step 1: Put the values of the first array in a set. A set finds a value in constant time.
        java.util.Set<Integer> first = new java.util.HashSet<>();
        for (int value : a) {
            first.add(value);
        }

        // Step 2: Keep the values of the second array that are in the first set. TreeSet sorts them and removes duplicates.
        java.util.TreeSet<Integer> common = new java.util.TreeSet<>();
        for (int value : b) {
            if (first.contains(value)) {
                common.add(value);
            }
        }

        // Step 3: Make the output text.
        if (common.isEmpty()) {
            return "none";
        }
        StringBuilder text = new StringBuilder();
        for (int value : common) {
            text.append(text.length() == 0 ? "" : " ").append(value);
        }
        return text.toString();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        int sizeB = scanner.nextInt();
        int[] b = new int[sizeB];
        for (int i = 0; i < sizeB; i++) {
            b[i] = scanner.nextInt();
        }
        System.out.println(solve(a, b));
    }
}