package Maths;

public class PiNilakantha {

    // Calculates Pi using Nilakantha's infinite series
    // Method 2 in the following link explains the algorithm
    //https://en.scratch-wiki.info/wiki/Calculating_Pi


    public static void main(String[] args) {
        assert calculatePi(0) == 3.0;
        assert calculatePi(10) > 3.0;
        assert calculatePi(100) < 4.0;

        System.out.println(calculatePi(500));
    }


    /**
     *
     * @param iterations number of times the infinite series gets repeated
     *        Pi get more accurate the higher the value of iterations is
     *        Values from 0 up to 500 are allowed since double precision is not sufficient
     *        for more than about 500 repetitions of this algorithm
     * @return the pi value of the calculation with a precision of x iteration
     */
    public static double calculatePi(int iterations) {
        if (iterations < 0 || iterations > 500) {
            throw new IllegalArgumentException("Please input Integer Number between 0 and 500");
        }

        double pi = 3;
        int divCounter = 2;

        for (int i = 0; i < iterations; i++) {

            if (i % 2 == 0)
                pi = pi + 4.0 / (divCounter * (divCounter + 1) * (divCounter + 2));
            else
                pi = pi - 4.0 / (divCounter * (divCounter + 1) * (divCounter + 2));

            divCounter += 2;
        }
        return pi;
    }
}