Plus One on a Digit Array

/*
 * Problem : Plus one.
 * Input   : n, then the digits.
 * Output  : The new digits.
 * Approach: Carry from the right.
 * Time    : O(n)
 * 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(int[] a) {
        // Step 1: Start at the last digit and add the carry. Work on a copy.
        int[] digits = a.clone();
        for (int i = digits.length - 1; i >= 0; i--) {
            // Step 2: A digit below 9 takes the one, and we are done.
            if (digits[i] < 9) {
                digits[i]++;
                return digits;
            }
            // Step 3: A 9 becomes 0 and the carry goes to the next digit on the left.
            digits[i] = 0;
        }
        // Step 4: All digits were 9. The result is 1 followed by zeros.
        int[] result = new int[digits.length + 1];
        result[0] = 1;
        return result;
    }

    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();
        }
        System.out.println(Arrays.stream(solve(a)).mapToObj(String::valueOf).collect(Collectors.joining(" ")));
    }
}