package bitcoin;

import static java.lang.Math.exp;
import static java.lang.Math.pow;

public class AttackerSuccessProbability  {

    public static double AttackerSuccessProbability(double q, int z)
    {
        // p = probability an honest node finds the next block
        double p = 1.0 - q;
        double lambda = z * (q / p);
        double sum = 1.0;
        int i, k;
        for (k = 0; k <= z; k++)
        {
            double poisson = exp(-lambda);
            for (i = 1; i <= k; i++)
                poisson *= lambda / i;
            sum -= poisson * (1 - pow(q / p, z - k));
        }

        return sum;
    }

    public static void main(String[] args)
    {
        // q = probability the attacker finds the next block
        double qs[] = {0.1, 0.3, 0.5};

        for( int j = 0; j < qs.length; j++) {
            double q = qs[j];

            System.out.println("q=" + q);
            for (int z = 0; z < 10; z++) {
                System.out.println(String.format("z=%d, prob=%f", z, AttackerSuccessProbability(q, z)));
            }
            System.out.println("");
        }
    }
}