Solution to Monte Carlo problem for Coding Dojo Feb 2012 by Mims H. Wright

montecarlo.java

import java.io.*;

/**
* @author Mims H. Wright - mims@mimswright.com
*/
class montecarlo {
	
	// To run, on command line type:
	// javac montecarlo.java
	// java montecarlo
	
	public static void main ( String[] args) {
		int reps = 0;
		
		//  read the number of reps from the command-line
		System.out.println("Enter number of repititions then press enter.");
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    try {
	         reps = Integer.parseInt(br.readLine());
	    } catch (IOException ioe) {
	         System.out.println("Error reading reps!");
	         System.exit(1);
	    }
		System.out.println("Calculating π in " + reps + " steps.");

		int i = 0, inCircle = 0;
		double x = 0.0, y = 0.0, d = 0.0;
		while (i++ < reps) {
			// generate a random point
			x = Math.random();
			y = Math.random();
			// Find the distance from the origin. 
			d = Math.sqrt( x*x + y*y );
			// If it's less than the radius of the circle, it's inside the circle. 
			inCircle += d < 1 ? 1 : 0;
		}
		
		double pi = (double) inCircle / reps * 4.0;
		System.out.println("Pi is roughly " + pi + " ( " + inCircle + "/" + reps + ")");

		System.exit(0);
	}
}