Stream.mapMulti: Repeat Each Number

/*
 * Problem : Repeat each number.
 * Input   : n and the numbers.
 * Output  : The repeated numbers.
 * Approach: Nested loops
 * Time    : O(sum)
 * Space   : O(sum)
 * 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: Count the output size, then fill the result array. Every number x is written x times.
        int total = 0;
        for (int value : a) {
            total += value;
        }
        int[] out = new int[total];
        int at = 0;
        for (int value : a) {
            for (int i = 0; i < value; i++) {
                out[at++] = value;
            }
        }
        return out;
    }

    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(" ")));
    }
}