codehunter

codehunter.m

%Marc Ferradou
%v0.0.1
%Licence: WTFPL 
%Date: 3/16/14
%This code is an answer to the BNP codehunter challenge. It tooks me about 2 hours and I picked Matlab for its simplicity to do the job.
%As easy as this code looks, I was actually one of the 20 winners. As we say, KIS.
%Read more here: https://graduates.bnpparibas.com/codehunter/crack-the-challenge/
%Result: this is a 29x29 transformation of a london (I believe) landscape
%with 3 Easter eggs.
%Note: I choosed matlab because it was in my opinion the quickest (in term
%of time consuming) language to code a solution to this challenge.
%I believe the first goal of this challenge was to finish on time so I didn't focus
%on the complexity or the exatitude of the algorithm.
%Warning: I am assuming that the unscranbled image is in the current folder
%with the name 'CodeHunter-Scrambled-image.bmp'. I couldn't upload the
%folder with the image due to upload size limit. Code won't work without
%it.

%You have to  have CodeHunter-Scrambled-image.bmp in the folder you are
%executing this code.
imgO=imread('CodeHunter-Scrambled-image.bmp');
%imgW is the imagine we will be working on.
imgW=imgO;
%nval is the number of transformation we want to apply.
nval=29;
sizeImg=size(imgO);
%This loop goes backward to undo the transformation.
for n=nval:-1:2
    %width of a tile without decimal, note that width=height.
    w=fix(sizeImg(1)/n);
    %row and column are just for lisibility.
    row=n;
    column=row;
    %Initial rotation
    rot=90;
    %We append the image row per row.
    imgAppendRow=[];
    for r=1:row
        %This is the current row we are working on.
        imgRow=[];
        for c=1:column
            %We select the good row and column and apply the rotation
            tile=imrotate(imgW((r-1)*w+1:r*w,(c-1)*w+1:c*w,:),rot);
            %Then we append it to the current row.
            imgRow=[imgRow,tile]; 
            rot=rot+90;
            if rot>270
            rot=90;
            end
        end
        %At the end of the current row, we check if we don't have to add
        %the missing pixel that were ommited by the removing of the decimal
        if (n*w<sizeImg(1))
           fixRow=imgO((r-1)*w+1:r*w,column*w+1:sizeImg(1),:);
            imgRow=[imgRow,fixRow]; 
        end
        imgAppendRow=[imgAppendRow;imgRow];
    end
    %Once all row have been treated we check if there are extra pixel at
    %the bottom to add.
      if (n*w<sizeImg(1))
           fixBottom=imgO((row)*w+1:sizeImg(1),1:sizeImg(1),:);
            imgAppendRow=[imgAppendRow;fixBottom]; 
      end
    %We change the image we are working on with the one we just created
    %with the transformation.
    imgW=imgAppendRow;
end
imwrite(imgW,'CodeHunter-Unscrambled-image.bmp');