// Sum3.java

class SumThread extends Thread {
    private int from, to, sum;

    public SumThread(int from, int to) {
        this.from = from;
        this.to = to;
        sum = 0;
    }

    @Override
    public void run() {
        for (int i = from; i <= to; i++) {
            sum += i;
        } 
    }

    public int getSum() {
        return sum;
    }
}


public class Sum3 {
    public static void main(String args[]) {
        if (args.length != 3) {
            System.out.println("Pass threads, start and end.");
            return;
        }

        // get arguments
        int num_threads = Integer.parseInt(args[0]);
        int from = Integer.parseInt(args[1]);
        int to = Integer.parseInt(args[2]);

        // an array of threads
        SumThread [] threads = new SumThread[num_threads];

        // fill in the start/end ranges for each
        int step = (to - from) / num_threads;
        for (int i = 0; i < num_threads; i++) {
            int start = from + step * i;
            int stop = (start + step) - 1;

            // make sure we go all the way to the end on last thread
            if (i == (num_threads - 1)) {
                stop = to;         
            }

            System.out.printf("Thread %d sums from %d to %d.\n", i, start, stop);
            threads[i] = new SumThread(start, stop);
        }

        // start them all
        for (int i = 0; i < num_threads; i++) {
            threads[i].start();
        }

        // wait for all the threads to finish!
        try {
            for (int i = 0; i < num_threads; i++) {
                threads[i].join();
            }
        } catch (InterruptedException e) {
            System.out.println("Interrupted");
        }

        // calculate total sum
        int total_sum = 0;
        for (int i = 0; i < num_threads; i++) {
            total_sum += threads[i].getSum();
        }

        System.out.printf("The sum of %d-%d is %d.\n", from, to, total_sum);
    }
}