I've been really enjoying the Kropki puzzles both in Sudoku Xtra and now the 200 series, but just wondered if I was missing anything obvious with getting started on some of the puzzles?

For instance, in the 200 series (which I've only just started) I went straight for puzzles 2, 3 and 4 because there were plenty of the black dots in there. Obviously where there are 3 black dots in a row they can't include 3 and 6, so if there is another separate black dot, that has to be for numbers 3 and 6. (Hope that makes sense)

Similary, if the black dots in any 3 x 3 grid cover six of the squares, the remaining three squares have to be 5, 7 and 9, which also gives you a starting point.

However, I haven't worked out any strategies for where to start the puzzles that contain more white dots and very few black ones. Am I missing something obvious?

Hi Christine

I'm pretty sure I'm missing some strategies as well and will watch this post closely!

What I've worked out so far is:

Where two black circles share a cell the possibilities can only be 2 & 4.

Where black and white circles share a cell, 1 is elminiated and 9 (obviously) from that cell, although you might get the L-shape cross into another block where 1 could work.

Your 5, 7 9 observations

Where two white circles share a cell in a block, 1 & 9 are eliminated from that cell.

For cells with no black or white circles, those numbers can't be doubled or consecutive.

For puzzle 1 in the 200 book, my starting point was the bottom row of the central blocks, particularly the right block. There's a nice clutch of consecutive numbers, plus a helpful black circle. 1&9 are eliminated from the bottom row of that block, so you know they go elsewhere in the block and along the row. There were probably easier ways to get clues, but me, in my typical long winded, methodical fashion, concentrated on the cell with the black circle and a process of elimination left just 3 & 4 for that cell. I then looked at the consecutive combinations for 3 & 4, starting with 3, 4 & 5. As it turned out, the remaining numbers for that block invalidated the non-consecutive rule. That left 4 as the number to go in the cell with the black circle, giving a nice sprout and more clues.

I am sure there are easier ways to go about things, though, and will be eagerly waiting for strategies others use!



Edited 1 time(s). Last edit at 12/03/2012 01:17AM by Marilyn.

Thanks for all that advice Marilyn - there were one or two pointers there that I hadn't thought of. I'll go back and have another look at puzzle 1 now.

I found both your comments interesting, Christine and Marilyn, thanks for your ideas.

I, too, don't have many strategies for the Kropki and try to come to each new one with no preconceived ideas. In one puzzle as there were 2 sets of black dots in one row I assumed one had to be the 1248 and the other 36 and it was ages before I discovered they weren't!

The only additional point I can add is that if there is a black, white, black consecutively, then there has to be a 3 with either a 2 or 4 'inside' and one of the 'outer' numbers has to be 6. I used this more than once in puzzle 3 of the 200 series.

Otherwise, I don't find it helpful to fill the whole grid with possibilities, as I can't see 'the wood for the trees'!! (I do this of course for some of the other puzzles) So I try possibilities separately until I find a number that I can fix, then I'm away

Hope this makes sense!

This is a useful thread. Thanks for the tips. I have found that I do a lot of "if that is a .... then that must be a ..... etc" and follow the route until it breaks down and can be eliminated. Not very satisfying but it works. The puzzles seem to be slow to start but then move quickly once I have found a reliable starting point. I will try some of the strategies above now. I haven't done too many Kropki's yet but have so far completed all that I have started so quite satisfying.

The main reason I haven't done too many as I have been spending most available hours trying to crack the wonderfully challenging Inequalities (as I mentioned elsewhere). Am thinking of starting a thread for sharing with other "sufferers". Anyone out there?

So far I have completed just 7 out of the first 25!! Not a great success story but my determination knows no bounds. I have now been driven to the lengths of getting my long suffering partner to check all the numbers placed so far in the first 18 unfinished ones (not many at all in some cases!). I have inked them in if correct, rubbed out all pencilled in "possibles" and am starting them all again afresh from that point. Desperate measures. I think this book might outlive me at this rate of progress. Love it though. Tips and success stories very welcome. If anyone hasn't started them yet the 7 puzzles I have so far finished (and therefore possibly a slightly easier place to start maybe) are 3, 4,10,13, 19, 24, 25.

Yes, it is great you started this thread, Christine. When I first started doing Kropki from the magazine I used to put in loads of possibilities until I couldn't make sense of anything, rub out all the pencil markings and start again! Certainly the tips, slowing down, and thinking a bit more are helping me get through puzzles now with minimum marking of possibilities, so far. I still need to write things down, as if I have to see little numbers before I can think, but it's getting better!

Elisabeth, that's a great tip and came along just in time to give me a great start for puzzle 6 in the 200 book. You can expand on that if you come across a black, black, white, black consecutive sequence. The 3 & 6 can be immediately placed, with either a 1 or 8 at the other end!

Sue, I haven't done Inequalities in ages. I wasn't good with them at all. In fact, I blame them for getting me in the habit of filling grids with loads of possibilities. If you do start an Inequalities thread, I'll read it with interest. Might even pick up the puzzle again if I can learn strategies from everyone else's hard work!

Thanks for all the tips everyone - they are coming in very useful.

Sue - I have to admire your perseverance with the inequalities. I have put my book down for the moment in favour of some of the other 200 series puzzles, but am determined to pick them up again and have another bash. I don't like to be beaten. I've made a note of the ones you have completed and will let you know if I get anywhere with any different ones!

Hi Christine

Please do let me know your progress. I have now attempted, and (mostly) reattempted, all of the first 50 with enough success to make me continue at least. I have now completed 22 of them, rarely on the first attempt tho. They do not seem to get any harder which is a relief. Last night I managed no 49 on first attempt and in record time which was very satisfying, and very surprising! No 15 is particularly frustrating as I have 5/6 numbers placed in every box and still can't finish it! Nil desperandum.

I look forward to hearing of progress of others. Thank you Gareth for such a challenge. Tips welcome.

Sue

Hi Sue

Well done on solving so many of the first 50 puzzles. You have obviously got a better brain than mine. I put my equality book aside for a while in favour of some of the easier books Sudoku XV, Arrow, Kropki and even the Mystery Killer Sudoku Pro. After reading your post I've dug out the inequality book again but am really struggling with them. I've only completed four so far and have many of them started and then put down. I have a feeling they are going to prove a bit too much for me (I hate that - I don't like to be beaten). I'm not ready to give in yet though and will keep persevering and will let you know if I get any of them solved! Good luck and keep plugging away.

Gareth - perhaps a pre-quel edition with some easier ones?!!!!!

You're going great guns, Sue, well done. The last time I did inequalities was back in the Sudoku Pro magazine. Since reading all the posts about the 200 book, I've gone from being alarmed, to curious, to trying some inequality puzzles from the Sudoku Extra magazine, to ordering the 200 book! I don't remember why I stopped doing them, but I find I'm enjoying them again! When the book arrived, I dipped in and out of puzzle 1 for 2 days (hee hee) before finishing it. I'm currently on puzzle 2 which so far has got off to a good start. I find I enjoy inequalities more in small doses, once the initial groundwork has been done, e.g. while having a cup of tea or during an advert on tv, as the eyes are fresher and pick up on things I missed previously. I do prefer to try and finish one puzzle before starting the next, but we'll see how that goes!

Christine, any tips for the Arrow puzzles? Maybe a new thread should be started for this! I've done these in the past and enjoyed them enough to get the 200 book and the 101 Arrow Samurai book, but now my mind is a complete blank with them, and I haven't managed to finish puzzle 1 in the 200 book yet!