import java.util.Scanner;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicReference;
class IntegralCalculator implements Runnable {
private final double a, b;
private final AtomicReference<Double> totalArea;
private final CountDownLatch latch;
public IntegralCalculator(double a, double b, AtomicReference<Double> totalArea, CountDownLatch latch) {
this.a = a;
this.b = b;
this.totalArea = totalArea;
this.latch = latch;
}
@Override
public void run() {
double width = ...
// The height of the rectangle is the value of the function at the midpoint
double height = ...
// f(x) = x^2
double area = ...
totalArea.accumulateAndGet(area, Double::sum);
// decrease count of latch here
...
}
}
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
double a = scanner.nextDouble();
double b = scanner.nextDouble();
int n = scanner.nextInt();
AtomicReference<Double> totalArea = new AtomicReference<>(0.0);
CountDownLatch latch = new CountDownLatch(n);
double width = (b - a) / n;
for (int i = 0; i < n; i++) {
double x1 = a + width * i;
double x2 = x1 + width;
new Thread(new IntegralCalculator(x1, x2, totalArea, latch)).start();
}
try {
// wait
...
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(totalArea.get());
}
}
