## Times Killer 30-9-05

All about puzzles in newspapers, magazines, and books
To afjt:
The Sept 28 killer is actually a "Killer X" (i.e. no repetition on the 2 main diagonals). So with that in mind you could get a unique solution.

To all:
Regarding the Sept 27 killer, I've worked it out by hand and found it does have 1 unique solution only, though I shamelessly applied T&E more than a few times... (Is it really shameful to try T&E on that puzzle?)

That said, I think it's a perfectly valid puzzle, and when Mr. Tetsuya Nishio claimed that he could make a killer sudoku that a champion needs 6 hours to solve, this one strikes pretty close on that line (of course it's computer generated...) Surely a very tough challenge for everybody to sharpen their Killer solving techniques (one of the contradiction branch goes all the way to fill almost the whole grid and only fails on one single cage...)

PaulIQ164 wrote:I got those 3 cells, but it was trial&error really (though I doubt the boundaries are as clear in Killers as the already fuzzy sudoku ones). The 5 in row 4 has to be in the 18-cage, and there's only two ways to make 18 in 5 cells using a 5 (5+1+2+4+6; 5+1+2+3+7). The latter leads to an impossibility when you try to fill box5, so it must be the first alternative, which lets you fill the box correctly.
Paul, I think you made a mistake there. 5+1+2+3+7 actually leads to the correct solution, and 5+1+2+4+6 instead leads to a contradiction eventually, but I could fill box 5 and go a long way before that happens. In fact the contradiction that almost had the whole grid filled is actually one of the branches from there. To show you, consider the following configuration of rows 4-6:

Code: Select all
`{123} {123} {23}  {8} {7} {4} {9}   {56}  {56}{678} {678} {678} {9} {3} {5} {24}  {124} {124}{45}  {45}  {9}   {2} {6} {1} {378} {378} {378}`
It still takes an effort to work all possibilities to contradiction from here...
Last edited by udosuk on Fri Oct 07, 2005 12:01 pm, edited 2 times in total.
udosuk

Posts: 2698
Joined: 17 July 2005

udosuk wrote:The Sept 28 killer is actually a "Killer X" (i.e. no repetition on the 2 main diagonals). So with that in mind you could get a unique solution.

Thanks for that. Clearly if it is a Killer X then it does have a unique solution, but when I look at the puzzle archive, nowhere does it tell me that !
afjt

Posts: 82
Joined: 07 September 2005

...and had I known it was a Killer X, I might have found it easier than I did ! As it was I got all the way through (apart from the 2<-->3 issue I mentioned) without looking at the diagonals.
afjt

Posts: 82
Joined: 07 September 2005

udosuk wrote:Paul, I think you made a mistake there. 5+1+2+3+7 actually leads to the correct solution, and 5+1+2+4+6 instead leads to a contradiction eventually, but I could fill box 5 and go a long way before that happens. In fact the contradiction that almost had the whole grid filled is actually one of the branches from there. To show you, consider the following configuration of rows 4-6:

Code: Select all
`{123} {123} {23}  {8} {7} {4} {9}   {56}  {56}{678} {678} {678} {9} {3} {5} {24}  {124} {124}{45}  {45}  {9}   {2} {6} {1} {378} {378} {378}`
It still takes an effort to work all possibilities to contradiction from here...

Yeah, you're right. I looked at it again and I can't work out what I thought I was talking about.
PaulIQ164

Posts: 533
Joined: 16 July 2005

Obviously I made a mistake too! Will reprint the puzzle and have another go some time.

BTW - should we post messages about DJApe's puzzles elsewhere? Perhaps we need a separate category for Killer Sudokus?
CathyW

Posts: 316
Joined: 20 June 2005

I knew the Sept 28 one was a Killer X because I downloaded it from the blog/homepage on that day instead of from the archive like you did. Of course it'd be nice if there were a pale "X" across the grid like the one on Oct 6... or djape could add a "(killer X)" after that link in the archive?

P.S. Let's post messages in djape's page on http://www.djape.net/sudoku/wp/?p=49#comments instead... it's really odd to discuss his puzzles in the Times section in this forum... I'm going to put some more tips there right now.
udosuk

Posts: 2698
Joined: 17 July 2005

### djape

i have posted another logical step to the above killer. Anyone care to continue? (link above)

Dom
domt

Posts: 16
Joined: 01 September 2005

### Killer? Whazzat?

What the hell is a KILLER Sudoku anyway? Does it cut you when you try and sovle it? What if you're on the bus, does it attack the driver? I thought i hated doing Sudoku's when i first saw one. Then i tried it and failed. Then i tried it and worked it out. Real proud of myself till i got here. You guys are Mathmaticians for sure. Well i majored in Englich-I mean English, and it took me two days to do an LA times one. Then i became hooked. Thinking i could solve any puzzle. Now? Im scared again. Thanks. Thanks a lot.
magrurry

Posts: 2
Joined: 08 October 2005

Englich graduates - so panicky and emotional.
Karyobin

Posts: 396
Joined: 18 June 2005

Anyhow, if you really need to know, Killer Sudokus are explained here: http://www.timesonline.co.uk/article/0,,7-1757275,00.html
PaulIQ164

Posts: 533
Joined: 16 July 2005

### Sept 28 Killer from www.djape.net

afjt wrote:
udosuk wrote:The Sept 28 killer is actually a "Killer X" (i.e. no repetition on the 2 main diagonals). So with that in mind you could get a unique solution.

Thanks for that. Clearly if it is a Killer X then it does have a unique solution, but when I look at the puzzle archive, nowhere does it tell me that !

Thanks to udosuk for clarifying this problem. When I started posting "X" puzzles I didn't print the diagonals but now I do, so you won't ever had a problem not knowing what the new puzzles are.
djape

Posts: 34
Joined: 27 September 2005

### Comments and solutions welcome at www.djape.net

udosuk wrote:I knew the Sept 28 one was a Killer X because I downloaded it from the blog/homepage on that day instead of from the archive like you did. Of course it'd be nice if there were a pale "X" across the grid like the one on Oct 6... or djape could add a "(killer X)" after that link in the archive?

P.S. Let's post messages in djape's page on http://www.djape.net/sudoku/wp/?p=49#comments instead... it's really odd to discuss his puzzles in the Times section in this forum... I'm going to put some more tips there right now.

I created a separate category just for this one puzzle on my blog. Feel free to post comments and your suggestions for logical steps to solving this puzzle at http://www.djape.net/sudoku/wp/?cat=10
djape

Posts: 34
Joined: 27 September 2005

### Getting it

It's not that I'm at any point getting stuck on the Killers; it's just that my (in my head) perfect logic always winds me up needing to put two 3s in a row, or whatever.

All of that and I still dont get it.
fish953

Posts: 3
Joined: 12 October 2005

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