Parallel Sum with Threads

/*
 * Problem : Process an array.
 * Input   : n, then n integers.
 * Output  : The total.
 * Approach: Split, sum in threads, join.
 * Time    : O(n / k)
 * Space   : O(k)
 * 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 long solve(int[] a, int k) {
        // Step 1: Each worker writes its result in its own place in this array. No two threads write to the same place.
        long[] partial = new long[k];
        Thread[] workers = new Thread[k];
        int chunk = (a.length + k - 1) / k;

        for (int w = 0; w < k; w++) {
            final int id = w;

            // Step 2: Each worker sums its own part: the indexes from id * chunk to (id + 1) * chunk.
            workers[w] = new Thread(() -> {
                long sum = 0;
                for (int i = id * chunk; i < Math.min(a.length, (id + 1) * chunk); i++) {
                    sum += a[i];
                }
                partial[id] = sum;
            });
            workers[w].start();
        }

        // Step 3: join waits until a worker is finished. After all joins, every partial sum is ready.
        long total = 0;
        for (int w = 0; w < k; w++) {
            try {
                workers[w].join();
            } catch (InterruptedException error) {
                Thread.currentThread().interrupt();
            }
            total += partial[w];
        }
        return total;
    }

    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 k = scanner.nextInt();
        System.out.println(solve(a, k));
    }
}