Boundary Value Test Inputs

/*
 * Problem : Boundary values.
 * Input   : Two integers low and high.
 * Output  : The test values.
 * Approach: A set of limits.
 * Time    : O(1)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;
import java.util.Arrays;
import java.util.stream.Collectors;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static int[] solve(long a, long b) {
        // Step 1: A TreeSet removes repeated values and keeps the values sorted.
        java.util.TreeSet<Long> values = new java.util.TreeSet<>();

        // Step 2: Just outside, on, and just inside each limit: the places where off-by-one mistakes hide.
        values.add(a - 1);
        values.add(a);
        values.add(a + 1);
        values.add(b - 1);
        values.add(b);
        values.add(b + 1);

        // Step 3: Copy the values to an array. The shared output code prints int values, which is enough for our range.
        int[] result = new int[values.size()];
        int index = 0;
        for (long value : values) {
            result[index++] = (int) value;
        }
        return result;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        long b = scanner.nextLong();
        System.out.println(Arrays.stream(solve(a, b)).mapToObj(String::valueOf).collect(Collectors.joining(" ")));
    }
}