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Two Puzzles (Not) from the Philly Sudoku Championship - onigame [entries|archive|friends|userinfo]

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Two Puzzles (Not) from the Philly Sudoku Championship [Oct. 25th, 2007|10:23 am]
Amid some of the writeups of the Sudoku Championship, I thought it might be interesting to share a couple of puzzles you didn't quite see at the championship:

This puzzle was my attempt to push the envelope just a little bit at what can be done with theming Sudoku puzzles. There's a small intuitive leap to figure out what to do with the letters, presumably why it was rejected. After you get the leap, the puzzle isn't too hard; it would be about a medium.

This was my first draft of the Q puzzle, which Thomas mentions in glow(er)ing words on his journal entry. I really like the symmetries in this first draft; as you can see, not only are the placements near-symmetric, but many of the actual digit selections are symmetric as well. This puzzle was something like the last one I composed, and there are two bits of non-sledgehammer logic that you need to make progress.

Spoiler 1 in ROT13
Nsgre cynpvat gur boivbhf frira va gur ybjre-evtug obk, ybbx pnershyyl ng gur avarf.

Fvapr n avar unf gb tb va gur ybjre-evtug obk, vg jvyy rvgure or va pbyhza frira be ebj frira. Juvpurire bar vg tbrf va, vg jvyy sbepr nabgure avar onfrq ba gur bar vg vfa'g va -- fb gurer'f rvgure n avar va ebj bar pbyhza frira be ebj frira pbyhza 1. Va rvgure pnfr, gur gbc-yrsg pbeare (ebj bar pbyhza bar) pna'g or n avar, gurersber gur avar va gur hccre-yrsg obk vf sbeprq gb or va bayl bar ybpngvba.

After that placement, you can use a lot of standard (sledgehammer) logic to get a grid that is about half-filled (specifically, 43 cells filled). At that point:

Spoiler 2 in ROT13
Ybbx ng gur sbhe pryyf va ebjf bar naq sbhe, pbyhzaf fvk naq rvtug.

Gur gbc gjb zhfg or sbhe naq fvk va fbzr beqre.
Gur obggbz yrsg bar zhfg or fvk be rvtug (vg pna'g or sbhe orpnhfr gurer ner bayl gjb fcbgf va gur pragre obk jurer fvk be rvtug pna tb).
Gur obggbz evtug bar zhfg or sbhe be rvtug.

Gurersber, ab znggre juvpu jnl lbh cynpr gur rvtug, gur fvk naq sbhe va gur gbc ebj ner sbeprq.

The version that actually made it to the competition had two more givens, which means that the second bit of logic isn't needed.

[User Picture]From: motris
2007-10-26 01:13 am (UTC)
The first Q puzzle (as we solved it with the two extra givens in box 3) will be a legendary puzzle as far as competition puzzles go. As I've been commenting to Tom C (the reigning Times of London champ), it is a puzzle where the non-sledgehammer logic comes at the right time so that guessing is really not so tempting but thinking through contradictions makes progress. Just as with Cihan's toroidal in Lucca, I'm glad to have graced a beautiful puzzle with a fittingly solid solution. If nothing else, the Q got everyone's attention at the competition, and I was being told by many people after the competition that they were still looking at it.
This second version, with the cleaned up shape, is even more of a beauty.

The Dial 7 for Philadelphia is a very cool idea but probably correctly nixed for a championship as it would favor those with outside puzzle experience too much. But to repeat myself, excellent puzzles and excellent themes. I just worry if you've set the bar too high for future years.
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From: (Anonymous)
2007-11-02 11:29 pm (UTC)

Apparent ambiguity in Dial 7 for Philadelphia

Obvious guess is that each letter is some digit, probably each letter a distinct digit, yielding H6P in the top centre and A9I in the bottom centre. E and D don't look much use, but P in {1, 7}, H in {2, 3, 7}, I in {2, 3, 5, 7}, A in {2, 3, 7, 8} and L % 3 != 0 follow readily enough, along with the centre row's 3 and 8 and a 6 in the bottom centre tile. The centre tile's central column comprises I, H and A, so one of these is 3. Since neither P nor H can be 8, the top left tile's 8 is in its bottom row, so neither L nor A can be 8; we can now infer an 8 below the bottom right A. The bottom right tile's bottom row and centre right must be E, L, P, H and we know L, P, H aren't 8, so now we have E = 8.

Logic failing my limited brain, I resorted to experimentation, with back-tracking facilitated by my noddy solver (http://www.chaos.org.uk/~eddy/craft/sudoku.html) and found PHILADE = 1257398 worked, albeit ambiguous in the placement of: 7 and 9 in the three left tiles, and of: 4 and 8 in the centre three tiles. I have not tried to determine whether the solution is unique in PHILADE.

It seems a shame to be left with ambiguity, but it was a cute puzzle :-)

(Reply) (Thread)
[User Picture]From: onigame
2007-11-02 11:38 pm (UTC)

Re: Apparent ambiguity in Dial 7 for Philadelphia

Heh. Your "obvious guess" is wrong.

Hint: Is the title of the puzzle trying to tell you anything?

(Reply) (Parent) (Thread)
From: (Anonymous)
2007-11-03 02:10 pm (UTC)

Re: Apparent ambiguity in Dial 7 for Philadelphia

Is the title of the puzzle trying to tell you anything?

Well, the letters of "dial" all appear in Philadelphia, "for" might be an allusion to 4, which is the length of "dial", 7 doesn't appear in the grid and is the number of distinct letters in Philadelphia, but I couldn't see any way to construe any of that as a clue. I did wonder whether this might have something to do with US telephone codes, but I know nothing of these. So I pursued what seemed obvious. It is nice to hear that the ambiguity I found could have served as a clue that I'd guessed wrong ;^)

Oh, and turning on "Check spelling during preview" seems to suppress "Don't auto-format"; or, at least, my markup is displayed (and "blockquote" is marked as a spelling error). I also seem to be failing the Turing test implicit in your anti-spam kaptchas :-}

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From: alexorize
2008-07-16 06:38 am (UTC)
The tic-tac-toe grid in the puzzle's middle turned a cute puzzle into a kind of masterpiece. My favorite part of the puzzle is that the "winning" column in the tic-tac-toe grid is 34D: Adults-only (XXX) - "And the winner is.
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[User Picture]From: nickbaxter
2007-11-19 09:47 pm (UTC)

Dial 7 for Philadelphia

Wei-Hwa over-delivered with so many attractive and challenging puzzles, that it's just not fair to say that the unused puzzles were "rejected".

But in the case of Dial 7 for Philadelphia, it's more precise to say that it was inappropriate. It's a fine puzzle, but requires some cultural knowledge to figure out what's up with those letters. I was trying to stick as closed as possible to standard Sudoku rules, so this one had no chance.


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From: domheyguy
2008-01-01 05:11 pm (UTC)

The 'ships in Philly & Dial 7

I really enjoyed your puzzles in the Philly Championships. (My best finish was 5th in the 2nd round and the "Q" puzzle really threw me for a loop.)

About "Dial 7," I came to the same conclusion that "Anonymous" did (it took me quite a while, btw). Since you say that conclusion is wrong, please explain the answer to me, if you would be so kind. I spent four years in Philly and still didn't get the "cultural reference" that Baxter referred to.


P.S.: I got a kick out of the fact that (presuming every letter represents a distinct digit--and 4 and 6 have no letter) the solution yields; P=1, H=2, A=3, I=5, L=7, E=8, and D=9, which spells out
"PHAILED," as I (and the Phillies) evidently did.
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From: jmargus
2008-11-14 02:15 am (UTC)

Philly Sudoku Championship

This game Sudoku is growing; it obviously has an international presence. We're faced with problems every day in life, and most of them have no perfect solutions. As the puzzle began to reveal itself and the scribbling grew more furious, it became clear that this wasn't just a game. Congratulations to Wei-Hwa Huang, National Sudoku Championship winner. Do us proud in the World Sudoku Championship in Slovakia so the guys from ABBA can be inspired to write a musical about you, too.
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