Java code to demonstrate the solution to Prisoners & Hats puzzle (http://randomsync.net/2011/09/puzzler-prisoners-and-hats-and-jungle.html)

PrisonerPuzzler.java

/*
 * http://www.cartalk.com/content/puzzler/transcripts/201127/index.html
 * http://www.cartalk.com/content/puzzler/transcripts/201127/answer.html
 */

import java.util.Random;

public class PrisonerPuzzler {
	static int SIZE = 30;

	public static void main(String[] args) {
		int correctGuesses = 0;
		StringBuffer pRow = new StringBuffer(SIZE);
		StringBuffer prevGuesses = new StringBuffer(SIZE - 1);
		char currGuess;

		Random rnd = new Random(System.currentTimeMillis());
		// ---print the series
		System.out.print("Series:\t");
		for (int i = 0; i < SIZE; i++) {
			if (rnd.nextInt(2) == 0) // 0=black, 1=white
				pRow.append('B');
			else
				pRow.append('W');
			System.out.print(pRow.charAt(i) + " ");
		}
		// ---strategy
		System.out.print("\nStrat:\t");

		for (int i = 0; i < SIZE; i++) {
			currGuess = guessStrategy(prevGuesses.toString(),
					pRow.substring(i + 1));
			System.out.print(currGuess + " ");
			if (currGuess == pRow.charAt(i))
				correctGuesses++;
			prevGuesses.append(currGuess);
		}
		System.out.print("\nCorrect Guesses=" + correctGuesses);
	}

	public static char guessStrategy(String prevGuesses, String remArr) {
		// random
		// Random rnd = new Random(System.currentTimeMillis());
		// if (rnd.nextInt(2) == 0) //0=black, 1=white
		// return 'B';
		// else return 'W';

		int numB = getNumOfChars(remArr, 'B');
		int numPrevB;
		if (prevGuesses.length() == 0) { // initial guess
			if (numB % 2 == 0)
				return 'W'; // if B is even, return W
			else
				return 'B'; // else return B
		} else {
			// strategy: if previously even number of people have said black,
			// and I see even black hats, I have a white hat, else black
			numPrevB = getNumOfChars(prevGuesses, 'B');
			if (numPrevB % 2 == 0) {
				if (numB % 2 == 0)
					return 'W';
				else
					return 'B';
			} else {
				if (numB % 2 == 0)
					return 'B';
				else
					return 'W';
			}
		}
	}

	/**
	 * @param arr
	 * @param ch
	 * @return number of times the specified char appears in the array
	 */
	public static int getNumOfChars(String arr, char ch) {
		int num = 0;
		for (int i = 0; i < arr.length(); i++) {
			if (arr.charAt(i) == ch)
				num++;
		}
		return num;
	}
}

Here's the output for one of the runs: (you're bound to get alteast 29 correct answers)

Series: B W B W B B B W W B W W W W B B W B B W W B B B W B W B W W
Strat: W W B W B B B W W B W W W W B B W B B W W B B B W B W B W W
Correct Guesses=29