For Robin

Sanjøy · Post by **Sanjøy** » Tue Dec 13, 2011 1:34 pm

robin wrote:Sanjoy, you are an utter barsteward for setting me this challenge!

Ferg · Post by **Ferg** » Tue Dec 13, 2011 1:39 pm

/paranoia.. you downloaded an executable from the govt and ran it? Maybe that was the test....

robin · Post by **robin** » Tue Dec 13, 2011 1:51 pm

I disassembled it first, then ran it in a VM

Ferg · Post by **Ferg** » Tue Dec 13, 2011 2:05 pm

It was more for comedic effect, but yes, I noted the use of the VM.

robin · Post by **robin** » Tue Dec 13, 2011 2:23 pm

I note that the page has now been updated with an explanation of how the challenge works. Gratifying to see that they didn't reveal anything I hadn't spotted along the way ...

Cheers,
Robin

Sanjøy · Post by **Sanjøy** » Fri Nov 23, 2012 1:30 pm

Another one for your Robin.

http://www.bbc.co.uk/news/uk-20456782

Sanjøy · Post by **Sanjøy** » Thu Dec 10, 2015 11:17 am

http://www.gchq.gov.uk/press_and_media/ ... -2015.aspx

robin · Post by **robin** » Fri Dec 11, 2015 5:11 am

Have you attempted to solve it or are you just baiting me

I think the grid shading problem is sodoku-esque.

For any line (row or column) let N be the number of numbers shown for that line. Let Xi be each of the numbers (i=1 to N).

Then if sigma(Xi,i=1..N) + N - 1 = 25 (25 is the length of each line, I think) then that line is completely defined - meaning there is only one possible solution.

sigma(Xi,i=1..N) means add up all the numbers.

For example, there is a row that is 1 3 1 3 10 2

N = 6
sigma(Xi,i=1..N) = 20

20 + 6 - 1 = 25.

So there is only one way of laying that row out (# means a shaded cell, _ means a white cell)

#_###_#_###_##########_##

For any line where that adds up to 24 there is one floating white cell to insert at the start or end or somewhere next to another white cell.

For lines that add up to 23 there are two floating white cells.

Etc.

So fill in all the 25s first. Then try as many of the 24s as you can. Then 23s. Etc. Each time you fill in a line you can go back and attempt to complete any intersecting higher order lines (i.e. if you've got some 24 columns left and you fill in a row then that might solve one or more of the columns).

Note also that lines with smaller N are easier to solve than lines with larger N because there are fewer spaces to insert the floating white cells.

It might help to mark white cells that are known to be white (as opposed to undecided) with a dot or something.

Or write some code that fills it in for you ... it's actually more fun than filling it in by hand unless you're very bored

Cheers,
Robin

Corranga · Post by **Corranga** » Fri Dec 11, 2015 9:58 am

A Nanogram is a bit of a let down following the previous puzzles

tut · Post by **tut** » Fri Dec 11, 2015 9:58 am

Damnation Robin, you just beat me to it.........

tut

JohnStewart · Post by **JohnStewart** » Fri Dec 11, 2015 6:55 pm

I've managed to solve this first stage. Started off on pen and paper, but realised that you need to mark some squares as definitely not black. After making a few mistakes I copied the image into paint on the PC and chose a different background colour and used the colour fill with left and right mouse clicks to fill in the squares.

What you end up with is a pattern that resembled one of those 3D barcodes. Scanned it with my phone which then opened a URL confirming the correct answer.

Step 2 is a round of 6 multiple choice questions each with 6 possible answers. I worked out 4 of them, and got another down to 2 options so just guessed a few times and got onto round 3 that I'm currently working on...

Post by **pete** » Sat Dec 12, 2015 10:41 pm

JohnStewart wrote:I've managed to solve this first stage. Started off on pen and paper, but realised that you need to mark some squares as definitely not black. After making a few mistakes I copied the image into paint on the PC and chose a different background colour and used the colour fill with left and right mouse clicks to fill in the squares.

What you end up with is a pattern that resembled one of those 3D barcodes. Scanned it with my phone which then opened a URL confirming the correct answer.

Step 2 is a round of 6 multiple choice questions each with 6 possible answers. I worked out 4 of them, and got another down to 2 options so just guessed a few times and got onto round 3 that I'm currently working on...

Millie is VERY EXCITED about this, we just got through L1 and she can barely sleep so keen is she to solve the next ones...

robin · Post by **robin** » Mon Dec 14, 2015 9:51 am

They can be very addictive - good to hear she's interested in solving the puzzle. See if you can get her into hacking - if you want a job at GCHQ the easiest way to get it is to hack your way into their payroll system and add yourself

JohnStewart · Post by **JohnStewart** » Mon Dec 14, 2015 5:35 pm

There are 5 levels in total, and the last level has a number of different puzzles, but it does say that they don't expect you to solve them all.

One of the puzzles (sum) is really easy using Roman Numerals, but there are others such as a word search, cipher decryption, suduko, a logic puzzle and some graphical ones as well. I've got anwers to a couple of them (I think), but struggling with most of the others.

Sanjøy · Post by **Sanjøy** » Tue Feb 02, 2016 1:38 pm

http://www.theregister.co.uk/2016/02/02 ... challenge/

Scottish Elises

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