Friday 21 August 2009

Friday Puzzles #11

OK, so this week I’ve taken a bit of inspiration from Thomas Snyder and his spin on a small sized Nurikabe puzzle. I think this is only fair, as he seems to have taken inspiration from my Friday puzzles idea; and although the weekly numbering appears to be concurrent, bear in mind I had a gap for a few weeks in June.

Anyhow, instead of localised island and sea grabbing – the mainstay of any Nurikabe solver’s arsenal – he’s created a puzzle which requires a little more global thinking. And he’s made it pretty damn hard in doing so. Which got me thinking about what I could come up with. Now, my effort is arguably a little less polished – but there is a rather delicious twist to this puzzle; a twist that pretty much cracks the puzzle in one (rather than having to slog through this by brute force). This is most definitely a toughie – enjoy!
    #015 Nurikabe – rated hard
All puzzles © Tom Collyer 2009

Friday 14 August 2009

Friday Puzzles #10

This week comes with a bit of a special theme. The number 10. It’s also very special in that I have managed to get this out and published on a Friday. Wow!

As regular readers may or may not know, last April I participated in the 4th World Sudoku Championships, hosted in a dusty provincial Slovakian town called Zilina. Much was made of the (lack of) quality of many of the puzzles – but one of the most enjoyable puzzles was a variant that appeared in the semi final:
    Puzzle M3 – World Sudoku Championship, Zilina 2009
The idea was simple – take a classic sudoku, and mark exactly where an adjacent pair of digits summed to 10. So if a 3 and a 7 were next to each other, a cage was drawn round and marked 10. The twist with this is the contrapositive inference – that is if no cage exists round a pair of adjacent cells, then the numbers inside cannot sum to 10! The puzzle itself had only one such pair of numbers marked – which made me wonder if actually you could go one better and perfect the puzzle.

Well, it turns out you can. After a lot of painstaking work to first even find a valid solution grid, I then wrestled with the task of making a decent puzzle – with my given visual theme. The result isn’t particularly challenging – though not totally trivial.

I do also have a couple of very hard puzzles too. They turned out to be hard almost by chance – they certainly aren’t a particularly pleasant solve in my opinion and so I haven’t bothered publishing them. Anyhow – without further ado, here’s the preamble: place the digits 1-9 in each row column and marked 3×3 box. Digits in adjacent cells may not sum to 10.
    #014 No Tens Sudoku – rated easy
All puzzles © Tom Collyer 2009. Well, obviously excepting the world championship puzzle above. I have no idea who to credit that to – and whilst used without permission, I’d like to think that demonstrating it would come under fair use. Anyhow, please respect the rights of the author.

Friday 7 August 2009

Friday Puzzles #9

Here’s a toroidal nurikabe puzzle. Ditto the comment for toroidal masyu – strictly speaking, removing the boundaries of the puzzle actual lifts a restriction rather than imposes one. However, having to change your thinking to deal with identification spaces isn’t the easiest thing in the world to do if you aren’t used to it!
    #013 Toroidal Nurikabe – rated easy
All puzzles © Tom Collyer 2009

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