Monty Hall Skeptics

For Monty Hall Skeptics (who are also computer literate), here is Java code that executes the Monty Hall problem:

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Results of 1,000,000 tests:

Stay Pat: you win 33.3166% of the time.
Switch: you win 66.6835% of the time.

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Code:

import java.text.*;

public class MontyHall {
    static void main(String[] args) throws java.io.IOException {
       System.out.println("Starting simulation");
       NumberFormat percent = NumberFormat.getPercentInstance();
       percent.setMinimumFractionDigits(6);
       int stayPatStrategy = 0;
       int switchStrategy = 0;

      // for simplicity, we always pick door one, but we randomly assign the caddy so it doesn't matter.

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

            // pick caddy
            int caddy = getRandomNumberInRange(1,3);

            // see what would have happened had we stayed pat
            if (caddy == 1) {
                stayPatStrategy++;
            }

            // Monty picks a different door with a goat
            // to make it fair, we will pick randomly
            int goatDoor = getRandomNumberInRange(2,3);
            if (caddy == goatDoor) {
                goatDoor = (goatDoor == 2) ? 3 : 2;     // set to other door if caddy
            }
            int remainingDoor = (goatDoor == 2) ? 3 : 2;    // set to other door

            // we pick the remaining door. Is it the caddy?
            if (caddy == remainingDoor) {
                switchStrategy++;
            }

            // every so often, print results
            if ((i % 10000) == 0) {
                System.out.println();
                System.out.println("Stay Pat = " + percent.format(stayPatStrategy/(double)i));
                System.out.println("Switch   = " + percent.format(switchStrategy/(double)i));
                System.out.println("Total iterations: " + i);
            }
       }
    }

    static int getRandomNumberInRange(int start, int end) {
        double value = Math.random(); // 0 <= x < 1
        return (int)((value * (end-start+1)) + start); // truncates
    }
}

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