I do not like everything done by the Government Communications Headquarters (GCHQ), Britain’s electronic comms spymasters, but I have to give them credit for the artful way they approach their task. Many large organizations send out greetings cards at this time of year, but only GCHQ would turn them into a clever way to recruit codebreakers. This year GCHQ’s cards contain an intriguing brainteaser, which leads to yet more complex puzzles. Presumably the prize for anyone who correctly answers them all is a job whose existence cannot be confirmed because it is covered by the Official Secrets Act.
If you fancy that job, or just want to see if you are the equal of Britain’s electronic spies, it does not matter if your name was not on GCHQ’s Christmas card list. The puzzle is also available from GCHQ’s website, or you could just copy the image above. The puzzle consists of a 25 by 25 grid, and instructions for which squares should be colored black. The numbers listed tell you the ordered sequence of consecutive blocks of black squares in each row and column. For example “2 1 6” means the row or column contains a block of two consecutive black squares, then a single black square, and then a block of six black squares, with at least one white square between each block. To get you started, a few black squares have already been filled in. Can you complete the rest, and work out the meaning of their pattern?
Wannabe codebreakers have until January 31st to solve all the puzzles and submit their answer to a particular GCHQ email address. Good luck if you enter, though I suppose we will never know if you won…
