Indian Puzzle Championship

Information and discussion on Puzzle Competitions
nickdeller
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Re: Indian Puzzle Championship

Post by nickdeller » Mon 13 Sep, 2010 10:08 am

Not going to have time to do this one in competition myself - had a big Scrabble tournament at the weekend, which generally went badly (albeit with a 302-point move fulfilling one of my more cherished ambitions in the game!) - so I'll do it at leisure later on instead.

detuned
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Re: Indian Puzzle Championship

Post by detuned » Mon 13 Sep, 2010 11:25 am

My appeal over mistyping the key wasn't upheld - I can sort of understand, but the odds of entering a key with switched adjacent digits must be pretty big (note that they get a lot lower if the switched digits aren't adjacent).

Anyhow, an actual score of 1215, but a moral score of 1435. Bearing in mind I might have had the dominos and paint by numbers on another day I am a lot happier with my performance on this one than Evergreens2. More practice needed on skyscrapers and arrows for me though - it's not that I can't do them, it's more I think I lack the confidence to get them quickly and without making silly mistakes at the moment. I'm going to give that German skyscrapers things a go at some point, but are there any good collections of arrows puzzles out there?

I think there will have been a few (maybe 10-15?) finishers, but anything approaching that is fairly decent I'd have thought. Great job David!

Anyhow - to kick off a vague discussion, the skyscrapers I thought was quite nice - I didn't find it too hard once I got going. The polplotek I got afterwards by the tried and tested method of fudging it until it worked. Did anyone get this with a more pleasing solve?

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 12:33 pm

david mcneill wrote:Alan,

Just found out that I have been given credit for the Spot the Differences, so have to be happy. Scared to think how quickly Thomas and co may have solved these.

All the best,

David.
Congrats David.

1685 here - messed up the answer key to SFINKS, missed a double on Bridges, messed up Ploptek, due to reading the 4 in the bottom right corner as a line count rather than a corner count and was a gnat's whisker away from the last Sudoku (the equal one). Kind of glad in a way for the mistakes as I'd have hated to have got that close to finishing and not done so. Weird logic, I know, but it makes sense to me :P

Official scores should be out soon - I'd guess that a number of people will finish, especially sudoku specialists. It's kind of odd that a fairly hefty proportion of the points was given to Sudoku given that recently it's been mostly absent from the WPC. Still, the Divisible by 3 and Equals had a nice extra puzzley bit to them.

Anyway, fingers crossed for the results...

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 12:35 pm

detuned wrote:Anyhow, an actual score of 1215, but a moral score of 1435. Bearing in mind I might have had the dominos and paint by numbers on another day I am a lot happier with my performance on this one than Evergreens2. More practice needed on skyscrapers and arrows for me though - it's not that I can't do them, it's more I think I lack the confidence to get them quickly and without making silly mistakes at the moment. I'm going to give that German skyscrapers things a go at some point, but are there any good collections of arrows puzzles out there?
Don't know about a collection, but there's a dead tough one in WPC 2008 - can't remember the round, but it's the "each clue is actually 1 higher or lower" round.

I'd love to know how to tackle this one...

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Re: Indian Puzzle Championship

Post by PuzzleScot » Mon 13 Sep, 2010 1:00 pm

OK, competition is over - let the discussion on puzzles commence!

Poplotek -
The RHS 2&4 at the top were my way in.
All but one of the 2nd row, and 2 of the top row meant there had to be a N-pentomino shape at the top.
The turns restriction on col 2 meant the top 2 rows were clearly defined.
The corners in col 3 are now a given.
The bottom line can be filled in now (2 corners, length 3 means it's continuous).
The line coming down from the N-shape in col 5 can't turn to col 6 right away, so the turns on row 4 are now given (note no turns in col 2).
We now have all turns in col 3 too.
Col3 row 3 must go left (to avoid closing the loop), and can be continued round to complete left side.
The remaining segments in cols 4 & 5 are forced, and we're done.

Shield -
14 is either 9+5 (so 13 is 6+7) or 8+6 (13 is 9+4). 13 can't be 9+4, since you can't then make sum=8 on left side. So former arrangement is used.
9 and 5, then 3 & 0 can be filled in (can't be 6 after that diff=3, since it's needed for sum=13)
For sum=13, the 6 can't be adjacent to 5, so we can fill in 7,6 & 2.
We're left with 1,4,8. 4 can't go next to 3, so goes on left. 1 can't be next to 0. done.

Lovely puzzles, once you've had a chance to digest them properly. I'll admit I wasn't as elegant as this in the contest, but largely the same process.

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 1:38 pm

OK, so we're discussing the puzzles now, so I'll give a few more detailed thoughts.

FYI, I did (or thought I did) everything before even looking at the sudokus, as I knew these would take longer than I'd like. As it was, I "finished" the rest with an hour to spare. I did spend a lot of time gaping at the seemingly random point assignation (is LMI Fill harder than Bridges?) and the titles (why are the last five called variants). Can't say I recall anything that I was particularly stuck on, except in hindsight the Polpotek thingy. I'm having another go at that later.

I'm going to put some more detailed thoughts on solving Arrows puzzles as well, as this seems to be a non-starter for some people. I'll write out how I tackled this one. It wasn't basic, but wasn't too convoluted.

On to the sudoku - basic was OK, Killer's colour scheme made my eyes cross, but I got it out in a reasonable time. Irregular slowed me down - actually stopped it and did the divide by 3 instead and then came back to it. Spotted the way in to the equal sudoku a bit too late (it's the three linked cells on the right hand side) and had to take a guess to finish it in time - guessed wrong though.

Overall, good fun, a bit frustrating for me, but I think I did enough to be happy with it in hindsight. With a bit more luck though... maybe next time.

I'll put the Arrows stuff in the general puzzle discussion bit this evening, rather than here.

dickoon
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Re: Indian Puzzle Championship

Post by dickoon » Mon 13 Sep, 2010 3:15 pm

PuzzleScot wrote:Just quickly on the battleships - note that there are a total of 20 cells used by the ships, despite one of them being missing from the pictorial representation. Now add up the digits you see for each row/column, and deduce the values for the remaining rows/columns ;)
You have beaten me to it! That was the one thing that I was going to comment upon as a potential solving technique with more general application. However, I suspect that that puzzle was deliberately designed to have many empty rows that were only clued as empty by implication, and I'm not sure if it's a motif that can be used again, or with more general application, except if the puzzle has deliberately been designed for it to be possible.

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 3:20 pm

dickoon wrote:
PuzzleScot wrote:Just quickly on the battleships - note that there are a total of 20 cells used by the ships, despite one of them being missing from the pictorial representation. Now add up the digits you see for each row/column, and deduce the values for the remaining rows/columns ;)
You have beaten me to it! That was the one thing that I was going to comment upon as a potential solving technique with more general application. However, I suspect that that puzzle was deliberately designed to have many empty rows that were only clued as empty by implication, and I'm not sure if it's a motif that can be used again, or with more general application, except if the puzzle has deliberately been designed for it to be possible.
I have seen something similar before, but I'll be blowed if I can remember where. It wasn't completely taken up, but I think rows added to 20 and columns to 19, which was enough of a restriction, because, I think, there were some adjacent big numbers that pretty much governed what had to happen in the grid.

If I find it, I'll say where I found it.

Oh, and the results are up, at least if you login and go to http://logicmastersindia.com/IPC2010/score.asp

Tom won again (congrats if he reads this), David came 9th - the best UK finish. Congrats, David

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Re: Indian Puzzle Championship

Post by PuzzleScot » Mon 13 Sep, 2010 3:35 pm

Scared to think how quickly Thomas and co may have solved these.
Tom won again
"With 50 minutes to spare" is the answer!

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Re: Indian Puzzle Championship

Post by detuned » Mon 13 Sep, 2010 3:42 pm

drsteve wrote: Official scores should be out soon - I'd guess that a number of people will finish, especially sudoku specialists. It's kind of odd that a fairly hefty proportion of the points was given to Sudoku given that recently it's been mostly absent from the WPC. Still, the Divisible by 3 and Equals had a nice extra puzzley bit to them.
Wouldn't say the sudoku specialists did particularly well here - names I recognise from WSC's I think have all done well at WPC's before too, with the exception of the Americans Will B and Jason Z, who are surely unfortunate to be American or else would have been on as WPC team in most other countries. I'd guess Rohan Roa was otherwise best of the sudoku specialists, but with the Indian title now I suppose that tag isn't really fair any more. I'm gradually trying to get rid of that tag myself - my moral placing would have been equal 29th. Other names who are particularly good (better than me), including Jakub Ondrousek, Gourav Korde and Fred Stalder are all further back.

Also, I think we need to begin curing some sudokuphobia on these boards - If you had the others (ok forget about the polpotek for now) done in the hour, you could reasonably expect to have had 15-30 minutes worth of bonus, and perhaps even more. Have you a rough idea on your timings for each of the puzzles? The irregular I guess was trickiest, but you could mostly solve that with the Law of Leftovers.

Alan - I will go through your Polpotek solution later. Thanks for posting it!

Re LMI fill - took me four or five iterations to get this out, which was surprising to me as the USPC examples I did in the last few weeks I got out very quickly.

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 4:21 pm

detuned wrote:
drsteve wrote: Official scores should be out soon - I'd guess that a number of people will finish, especially sudoku specialists. It's kind of odd that a fairly hefty proportion of the points was given to Sudoku given that recently it's been mostly absent from the WPC. Still, the Divisible by 3 and Equals had a nice extra puzzley bit to them.
Wouldn't say the sudoku specialists did particularly well here - names I recognise from WSC's I think have all done well at WPC's before too, with the exception of the Americans Will B and Jason Z, who are surely unfortunate to be American or else would have been on as WPC team in most other countries. I'd guess Rohan Roa was otherwise best of the sudoku specialists, but with the Indian title now I suppose that tag isn't really fair any more. I'm gradually trying to get rid of that tag myself - my moral placing would have been equal 29th. Other names who are particularly good (better than me), including Jakub Ondrousek, Gourav Korde and Fred Stalder are all further back.

Also, I think we need to begin curing some sudokuphobia on these boards - If you had the others (ok forget about the polpotek for now) done in the hour, you could reasonably expect to have had 15-30 minutes worth of bonus, and perhaps even more. Have you a rough idea on your timings for each of the puzzles? The irregular I guess was trickiest, but you could mostly solve that with the Law of Leftovers.

Alan - I will go through your Polpotek solution later. Thanks for posting it!

Re LMI fill - took me four or five iterations to get this out, which was surprising to me as the USPC examples I did in the last few weeks I got out very quickly.
I'll never be cured of my sudokuphobia, dammit!

Seriously, my concern with a competition like this mixing them is that the "specialists" are significantly faster at the sudoku while people who prefer other varieties of puzzle didn't have a particularly big puzzle to pick up time on. Domino was the only time consuming puzzle in the rest of it, but I'm not sure anyone could do it particularly quickly. Still, it's all good practise. Oh, don't recall any problems with the Skyscrapers though, so maybe that was harder than I found it.

As for my sudokus, as I said before, I had an hour left at that point. I think, if memory serves, I'd knocked off the classic and killer in about 15-20 minutes, spent another 15 or so on the irregular until I got stuck, 10 minutes on the divisible by 3 one, mainly as I'd worked out in advance what the way into it would be, and then back to irregular for another 10 or so before it fell, first spotting what I'd missed, a 7 in the upper middle area, and then making an educated (and correct) guess. 10 minutes left to stare at the equals, when I spotted the way in after 5, but that didn't quite leave me enough time to solve it. To be absolutely honest, I thought I sudoku'd pretty well for me this time. Still would rather do almost anything else instead though...

GarethMoore
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Re: Indian Puzzle Championship

Post by GarethMoore » Mon 13 Sep, 2010 8:14 pm

I didn't do it live but did it in chunks today so I can't be sure how representative this really is, but in 2 and a half hours (which didn't include working out or typing in and checking keys) I did all of the puzzles except for the divisible-by-3-sudoku, equal to sudoku, irregular sudoku and spot the difference (which was horrible).

The slowest puzzle for me was the Arrows which took me 22.5 minutes - I really have no idea how to notate this nicely, and I spent nearly all my time counting how many arrows were pointing at squares rather than actually solving it (the logic was fairly straightforward and the one mistake I made was easy to see how to fix at the end). I've never done these before because frankly I think they're horrible, but I should probably learn how to do them far more efficiently than this! Anyone got any good hints? I'm sure it would be much easier with a computer program updating all the counts automatically. ;) Perhaps copying it out and changing each number as you place arrows is the way to go?

The dominoes took 13 minutes but I don't see how I could have done it any faster, and I wasted 5 minutes on the Shield by not reading the "non-consecutive" rule first. Apart from the first few moves I did Box 321 entirely by luck in 5 minutes, so perhaps I missed some logic there?

Poplotek was solved in a similar way to the snake tournament I did a couple of days ago, so it was interesting that I think that practice helped since I got this out with fairly well-organised guessing. I don't know why but conversely LMI Fill was proof of complete disorganisation since it took me over 8 minutes in which time I "proved it was impossible" no less than 4 times.

I initially messed up the killer sudoku (which normally I'm okay at) and had to start again, although I'd like to blame the unusual presentation if I can. :) It took me over 18 minutes, but was quite susceptible to the "45 rule". I was also a bit slower than my usual speed of 'pretty slow' on the Skyscrapers - 15 minutes - mainly because I missed the obvious; the logic was not too bad really.

On those I did I completely agree the points didn't reflect difficulty.

After time was up I tried the sudokus I didn't do and messed up the irregular and divisible by 3 and gave up on the "equal to" sudoku, so that was pretty awful really. In the divisible by 3 clearly the digits must sum to 3 in each group of 3 (which mathematical note I helpfully accidentally remembered by misreading the instructions anyway since "the number created" was suitably vague enough that I initially read it as "sum to") - is there some more powerful general observation that can be made too?

drsteve
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Re: Indian Puzzle Championship

Post by drsteve » Mon 13 Sep, 2010 8:20 pm

GarethMoore wrote:
The slowest puzzle for me was the Arrows which took me 22.5 minutes - I really have no idea how to notate this nicely, and I spent nearly all my time counting how many arrows were pointing at squares rather than actually solving it (the logic was fairly straightforward and the one mistake I made was easy to see how to fix at the end). I've never done these before because frankly I think they're horrible, but I should probably learn how to do them far more efficiently than this! Anyone got any good hints? I'm sure it would be much easier with a computer program updating all the counts automatically. ;) Perhaps copying it out and changing each number as you place arrows is the way to go?
There are two threads in the general discussion area, one started by Alan a while a go and one started by me today because I didn't spot Alan's. They both have suggestions as to how to annotate and solve Arrows

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Re: Indian Puzzle Championship

Post by Janix » Mon 13 Sep, 2010 8:30 pm

Enjoyed that - especially as it was straight after my birthday party (hic!).

Happy with my performance, except that I took three attempts at LMI fill, then typed in Brown instead of Drown losing 80 points (cunning use of Gzu not Guh sound in LoGic / Green) - Gareth that may explain your puzzlement,

I completely overlooked Fences, and went to type the answer in THREE seconds after the cut off, another 110 down, having started it with 4.5 minutes to go (almost Motris speed!). Please can anyone confirm that it was possible to get it right by just doing the right hand side - a bit weird (the only question that you didn't have to do nearly all of to solve...)

I also enjoyed Shield, especially at the second attempt when I remembered that 3 - 0 (= 3) is a valid number pair! However, I missed the Battleships announcement - I know it was in red as well - so was confused over lack of info and didn't do it :-(

So a nominal 885, but relatively pleased with the 695.

Really nice to see the full breakdown of everyone's results - errors and all!

Ken

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Re: Indian Puzzle Championship

Post by detuned » Mon 13 Sep, 2010 9:26 pm

drsteve wrote:
Seriously, my concern with a competition like this mixing them is that the "specialists" are significantly faster at the sudoku while people who prefer other varieties of puzzle didn't have a particularly big puzzle to pick up time on. Domino was the only time consuming puzzle in the rest of it, but I'm not sure anyone could do it particularly quickly. Still, it's all good practise. Oh, don't recall any problems with the Skyscrapers though, so maybe that was harder than I found it.
Well based on the scores, it seems that having only sudoku in your belt is a disadvantage - the people profiting were those at the top who as well as being really good sudoku solvers, are equally good puzzlers. I imagine they'd have had those 5 done in half an hour plus or minus a bit. I bet Thomas S was probably closer to 20.

It's quickly becoming apparent to me that to score really highly you really have to be a jack of all trades - and simply having one speciality isn't going to get you anywhere. You need that strong all-round repertoire. So whilst there were a few sudoku on this test, it wasn't going to help the specialists challenge at the top. In that respect, I think you'll only have to worry about contests with higher sudoku weightings than these - and given such contests are only likely to be sudoku-only contests I don't think you have much to worry about.

So whilst the set probably felt a bit standard to you (it didn't feel particularly challenging to me) , and unsure as to where you would be making up time for your sudoku disadvantage, you probably had 2-3 minutes per puzzle minimum on the so-called specialists.

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Re: Indian Puzzle Championship

Post by Fred76 » Tue 14 Sep, 2010 1:01 pm

detuned wrote:Other names who are particularly good (better than me), including Jakub Ondrousek, Gourav Korde and Fred Stalder are all further back.
I'm actually what may be called a sudoku specialist, as I do almost not participate in puzzle tournaments. Very few other puzzles interest me as much as Sudoku. I participated in this tournament because there were a large part of sudoku. I've solved sudoku part in about 35 minutes. Irregular was perhaps the hardest. Then I tried another 8 puzzles with certain types that I had already done and I knew rules (kakuro, skysrapers, ABCD, Hashi for example). Despite that there was still 40 minutes remaining, I had not time to continue. There are puzzles that I haven't even read the rules.

It is true that there was a big part of Sudoku in this tournament. For people who do not like that, it would be difficult. One should be a complete player to solve all the puzzles, but it's true that all those who have completed have also lot of experience in sudoku tournaments. It would have been interesting to see the score would have made someone like Ullrich Voigt, who is a puzzle master, but does not (to my knowledge) participate in sudoku tournaments.

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Re: Indian Puzzle Championship

Post by PuzzleScot » Tue 14 Sep, 2010 1:26 pm

Ullrich Voigt, who is a puzzle master, but does not (to my knowledge) participate in sudoku tournaments
That's maybe why we couldn't see his score on the door! (all results are here: http://logicmastersindia.com/IPC2010/score.asp)

I, and I know of others, aren't Sudoku fans, because we don't like to specialise in that one puzzle type.
In the 'early days', pre-sudokumania, sudoku puzzles were just as challenging as any other puzzle type to us.
However, since Sudoku was popularised, with practice those started to seem easy, and no longer a challenge to the sudoku specialists, hence the average difficulty level has risen in that single puzzle genre. Not having gone with the sudoku specialist popular wave, those puzzles are now hard to me.
Conversely, I believe the sudoku specialists find other puzzle types largely overwhelming because they are beyond their comfort zone, requiring an entirely new set of skills to solve. Hence, I believe, the low cross-over rate of puzzlers from globally popular Sudoku to general logic puzzles.

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Re: Indian Puzzle Championship

Post by Fred76 » Tue 14 Sep, 2010 2:45 pm

I understand your point of view.

In fact, if I imagine having to organize a puzzle tournament, I see two ways to manage sudokus:

1. The sudoku is an important part of the literature on the puzzles, but since there are many sudoku tournaments, it became an "independent practice". Sudoku fans have already "enough to eat" :mrgreen: so I will not put more sudoku than another type puzzles.
2. Sudoku is very popular, so if I put a good sudoku part in my tournament, it will attract new players to the puzzle tournament, they'll discover other types, and perhaps discover a passion for puzzles.

The two ways of doing things have their purpose, and I think it is good that there are tournaments with lot of sudoku and others without sudoku(or with a single grid).

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Re: Indian Puzzle Championship

Post by detuned » Tue 14 Sep, 2010 5:53 pm

I think a take a different point of view.

I think it's all a little too easy to dismiss sudoku out of hand, especially combining it with an air of anti-popularism. I don't think it's a question of "choosing to specialise" either. Actually, sudoku contests tend to have a large range of variations that, once you move away from thinks like killer, diagonal, irregular, start getting you solving in radically different ways. Many variants I've seen have involved amalgamating aspects from other WPC styles - for example snake and skyscrapers - the point is that you need a wide skill set to get a good result at a sudoku contest. You get very few classics only contests these days - and the fact that the only UK sudoku contest was classics only was part of my inspiration to write a proper sudoku contest. I hope that everyone here who gets a chance to have a go will do so as I think I've written a really good set of puzzles.

I think it's a complete red herring to talk about a cross-over from the sudoku world to the general puzzling world. Many of the best sudoku players (Thomas Snyder, Hideaki Jo, Michael Ley, Byron Calver, Nikola Zivanovic, our own David McNeill, the list goes on) aren't "specialists" at all. They are simply genuinely good puzzlers who have had no problems adapting to the sorts of things sudoku can throw up. Actually, when you consider the wide skill set you need to excel at a sudoku competition, I'd argue it's hardly any wonder that a lot of puzzlers have had a lot of success with sudoku. I'd also argue that there are actually very few "sudoku specialists" at all (or at least those who do very well at sudoku contests) - and of those that are I think it's simply a question of exposure. For example, Fred here hadn't even seen a lot of the puzzles on the IPC. I think that most of these "specialists", should they choose to get a little more exposure, would have no problems at all adapting to more general puzzles. I think this was the point David McNeill had in mind when trying to recruit everyone and anyone to WPC style puzzles when I first met him at the Times championship in cheltenham in 2006.

In my own personal case, before this current boom in puzzle contests, there was pretty much the USPC and the WPC and that was it. The USPC always used to happen on my birthday weekend so I could never give it a go - and this obviously shut the door on the WPC (although I recall Simon Anthony trying to get me involved with the championship in Minsk when there were apparently problems getting a team together). The first proper puzzle contest I did was the Evergreens in July, but I think I'm quickly getting the hang of things. OK I've subscribed to nikoli.com, and been constructing nikoli style puzzles for a while now, but there's been plenty of stuff that I'd not ever seen before.

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Re: Indian Puzzle Championship

Post by PuzzleScot » Tue 14 Sep, 2010 11:55 pm

I can only speak for myself. My interest in Sudoku peaked here in 2005 (see link to answer sheet), and waned thereafter.

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Re: Indian Puzzle Championship

Post by PuzzleScot » Thu 16 Sep, 2010 8:47 am

Back on topic. Divisible by 3 Sudoku.
I had a few shortcuts on this puzzle, but still struggled, so I'm wondering if I missed anything obvious?
Aside from the obvious 'divisible by 3 means sums to multiple of 3', I did this:

I wrote the numbers in 3 columns (groups) A,B & C:
A B C
1 2 3
4 5 6
7 8 9

Mathematically, Amod3 = 1, Bmod3 = 2, Cmod3 = 0.
Therefore, to choose 3 elements to have SUMmod3=0, we either need all 3 from the same group, or all 3 from different groups.
Thus the 3 members of each group (in each 3x3 box) must all be in a row/column, or all in different rows/columns.
If they were all aligned horizontally in any box, then the 2 other boxes in that row must also have their groups all aligned horizontally. (and conversely for vertically aligned).
Less obviously, all diagonal 3-digit numbers in each 3x3 also sum to 3, which is also helpful to know.

So with this 'insight', the TR box with a 5&8 (both from group B) means that the 2 MUST go in the TR corner of that box. Similarly, the 8 must be TL of TL box.

I don't know if anyone else used this grouping, or if I've missed some other shortcut, but it took me over 30 minutes to do anyway.

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Re: Indian Puzzle Championship

Post by detuned » Thu 16 Sep, 2010 10:02 am

Alan, you have the gist of the puzzle there. The key to it all is this effectively segregates the puzzle into 3 "easy" puzzles - the challenge is working out where the segregation comes in (not unlike sudoku islands, to put in a shameless plug here).

The way I looked at it was to first get the labellings of cells via A,B,C sorted (in practice I used 147, 258 and 369 pencilmarks, but whatever). The point is that when, in a 3x3 box you have definitely ascertained that one square is labelled A:

Code: Select all

...
..A
...
Then there are only two possible patterns to go by for that 3x3 box

Code: Select all

.A.
..A
A..
or

Code: Select all

A..
..A
.A.
.

Now, that a massive restriction from just one digit in a 3x3 box! If there's, say, a B digit in that 3x3 box in a different column and row, then it definitely fixes the labelling for that 3x3 box. E.g.

Code: Select all

A..
.B.
...

Code: Select all

ACB
CBA
BAC
So you can fairly quickly get the 3x3 boxes labelled by A/B/C (or as I had, with the 147, 258 and 369 pencilmarks). Once you have this labelling complete, much like sudoku islands, the fixing of the digits within these subsets is relatively trivial. This is where my notation came in handy: for example I had an A square already with a 7 in that row elsewhere, then I simply put in 14.

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Re: Indian Puzzle Championship

Post by PuzzleScot » Thu 16 Sep, 2010 10:21 am

Ah Ok, I was close then.

However, you do miss one obvious trap, that wasn't sprung here. The top 3 rows COULD have looked like this, couldn't they?

Code: Select all

AAA BBB CCC
BBB CCC AAA
CCC AAA BBB

detuned
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Re: Indian Puzzle Championship

Post by detuned » Thu 16 Sep, 2010 10:53 am

Yeah possibly - if it weren't for the top middle 3x3 box with the 2 and 1 on the same row. There was just enough information with the givens to see that such a trap was very probably unlikely after a quick scan - I went with the hunch rather than definitively satisfy myself that this was the case at the time.

In fairness with my slightly over simplified explanation - there IS a little bit of sudoku to do about half to 2/3 of the way in, fixing a 4 the middle right 3x3 box, and a 9 in the 3rd row.

drsteve
Posts: 727
Joined: Sun 27 Jun, 2010 7:23 am

Re: Indian Puzzle Championship

Post by drsteve » Thu 16 Sep, 2010 4:38 pm

That was exactly the same method I used - I'd considered the

AAA
BBB
CCC possibility was unlikely and thereafter it fell quite quickly.

The advantage of having the three easy puzzles in this was that when I went a little astray on placing the 369s, all I had to do was rub those out and still had 2/3 of the puzzle solved.

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