package blatt13;

public class SummierRunnable implements Runnable {
	
	private int sum, length, start;
	private int[] input;
	
	public SummierRunnable(int[] input, int start, int length) {
		sum = 0;
		this.length = length;
		this.start = start;
		this.input = input;
	}
	
	@Override
	public void run() {
		for (int i = 0; i < length; i++)
			sum += input[start + i];
	}
	
	
	
	public static int sum(int[] input, int numThreads) {
		if (numThreads <= 0)
			throw new IllegalArgumentException("at least one thread");
		
		Thread[] threads = new Thread[numThreads];
		SummierRunnable[] runs = new SummierRunnable[numThreads];
		
		int start = 0;
		for (int i = 0; i < numThreads-1; i++) {
			int length = input.length / numThreads;
			runs[i] = new SummierRunnable(input, start, length);
			threads[i] = new Thread(runs[i]);
			threads[i].start();
			start += length;
		}
		
		// letzter Thread separat:
		runs[numThreads-1] = new SummierRunnable(input, start, input.length-start);
		threads[numThreads-1] = new Thread(runs[numThreads-1]);
		threads[numThreads-1].start();
		

		for (Thread t : threads) {
			while (true) {
				try {
					t.join();
					break;
				} catch (InterruptedException exc) {}
			}
		}

		int sum = 0;
		for (SummierRunnable run : runs) {
			sum += run.sum;
		}
		
		return sum;
	}
	
	public static void main(String[] args) {
		int[] arr = {1,2,3,4,5,6,7,8,9};
		System.out.println(sum(arr, 1));
	}
}