Simulate a certain random walk; see http://math.stackexchange.com/questions/245122

Question245122.java

import java.util.Random;

public class Question245122 {
    final static Random random = new Random ();

    public static void main (String [] args) {
	int N = Integer.parseInt (args [0]);
	int ntrials = Integer.parseInt (args [1]);
	int count = 0;

	for (int n = 0;n < ntrials;n++) {
	    int pos = 0;
	    do {
		int d = (random.nextBoolean () ? 1 : -1) * (random.nextBoolean () ? 1 : 2);
		pos += d;
		if (pos == N)
		    count++;
	    } while (pos < N);
	}

	System.out.println (count / (double) ntrials);
    }
}