TheUnknownProblem

import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;

/**
 * Tuenti Programming Contest
 * Challenge 17: The ¿? Problem
 * @author alefhidalgo [at] gmail [dot] com
 */
public class TheUnknownProblem {

    /* Secret text */
    private static final String HIDDEN_STRING = "Good job crack! You have done well :) To finish this challenge you have to write the program that submits the following code: ";
    /* Secret code length */
    private static final int LONG_SECRET_CODE = 40;
    private BufferedImage image;

    /**
     * Constructor
     * @param image
     */
    public TheUnknownProblem(BufferedImage image){
        this.image = image;
    }

    /**
     * Get Hidden Code from image
     * @return
     */
    public String getHiddenCode(){
        int x = image.getWidth();
        int y = image.getHeight();
        StringBuilder sbLSB = new StringBuilder();
        for (int i = 0; i < y; i++) {
            for (int j = 0; j < x; j++) {
                int pixel = image.getRGB(j, i);

                int r = (pixel >> 16) & 0xff;
                int g  =(pixel >> 8) & 0xff;
                int b = (pixel) & 0xff;
                String sr = Integer.toBinaryString(r);
                String sg = Integer.toBinaryString(g);
                String sb = Integer.toBinaryString(b);
                /* Get Less Significative Bit and append in order BLUE,GREEN,REED*/
                sbLSB.append(sb.substring(sb.length()-1, sb.length()));
                sbLSB.append(sg.substring(sg.length()-1, sg.length()));
                sbLSB.append(sr.substring(sr.length()-1, sr.length()));
            }
        }
        StringBuilder decoded = new StringBuilder();
        for(int i=0; i<sbLSB.length();i+=8) {
         decoded.append((char)Integer.parseInt(sbLSB.substring(i,i+8), 2));
        }
        //get secret CODE
        int indexCode= decoded.indexOf(TheUnknownProblem.HIDDEN_STRING) + TheUnknownProblem.HIDDEN_STRING.length();
        return decoded.substring( indexCode ,indexCode + LONG_SECRET_CODE);
    }

    public static void main(String[] s) {
        BufferedImage image= null;
        BASE64DecoderStream decoder = new BASE64DecoderStream(System.in);
        try {
            image = ImageIO.read(decoder);
        } catch (IOException e) {
            /* Never should happen */
        }
        TheUnknownProblem theUnknowProblem = new TheUnknownProblem(image);
        System.out.println(theUnknowProblem.getHiddenCode());
    }
}