dump.java

public class Classifier{
	public static boolean[] stringToBoolean(String s){
		boolean[] b = new boolean[s.length()];
		for(int i=0; i<s.length(); ++i){
			b[i] = (s.charAt(i) == '1');
		}
		return b;
	}
	
	public static void main(String[] args){
		boolean[] testA = stringToBoolean("10011001");			
		boolean[] testB = stringToBoolean("");
		
		Classifier classifier = new Classifier(
			stringToBoolean("10011001"),
			stringToBoolean("01111000")
		);
		System.out.println(classifier.probabilityOfRetaliation);
		System.out.println(classifier.probabilityOfForgiveness);

		classifier = new Classifier(
			stringToBoolean("00000000"),
			stringToBoolean("11111111")
		);
		System.out.println(classifier.probabilityOfRetaliation);
		System.out.println(classifier.probabilityOfForgiveness);		
	}
	
	public final double probabilityOfRetaliation,
		probabilityOfForgiveness;
		
	/**
	Creates a classification of a after a game of b
	 */
	public Classifier(boolean[] a, boolean[] b){
		double slights=0, retaliations=0, forgivens=0;
		for(int i=2; i<a.length; ++i){
			// a cooperated then b defected.
			if(a[i-2] && b[i]){
				slights++;
				if(a[i]){
					forgivens++;
				}else{
					retaliations++;
				}
			}
		}
		probabilityOfForgiveness = forgivens/slights;
		probabilityOfRetaliation = retaliations/slights;
	}
}