killer sudoku - repeat digits if a sum box overlaps a block

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killer sudoku - repeat digits if a sum box overlaps a block

Postby steve » Thu Oct 20, 2005 1:47 pm

Some weeks ago, I noticed in the 'rules' for killer (dated 07.10.05) that it stated digits CANNOT be repeated in a dotted box. I wrote to the Times and said this was illogical and that it must be possible for a number to be repeated as long as the normal Sudoku rules are not broken. I was delighted that some days later (11.10.05) my new text was shown. However, the next day there was an editor's apology about the previous day's "misprint" and a statement that digits CANNOT be repeated.
I wonder why this could be! If it is simply a rule then OK but why; this makes the solving easier in some cases since certain permutations are not possible. In my thinking, to take an extreme example, if 2 entire columns were inside a dotted box, the total would of course be 90 but there must then be 2 of every digit inside the box.
Clearly, I am only talking about boxes that are NOT in a single column or row, e.g. an 'L' shape or more complex.

My rules would say simply:
Fill the grid so that every column, every row and every 3x3 box contains the digits 1 to 9.
The digits within the cells joined by dotted lines add up to the printed top left-hand figure.

Additionally, I would add, although it is not necessary:
Within each dotted line shape, a digit can be repeated if the normal row, column and 3x3 box rules are not broken.

I would love to hear if anyone has come accross this issue or indeed if anyone has found a killer where digits are repeated inside a complex shape.
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Postby PaulIQ164 » Thu Oct 20, 2005 1:52 pm

There was a lot (and I mean a lot) of discussion about this when the rules printed in The Times were changing every other day. The consensus is though, that digits indeed CANNOT be repeated in a dotted-line box. As you say, this isn't a logical consequence of the other rules; it is a separate rule in its own right.
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Postby udosuk » Thu Oct 20, 2005 4:36 pm

So you are the "culprit" for the Times indecision about the rules... (Don't worry, just kidding!)

I'll tell you why numbers must not repeat within the cages. This puzzle is not invented by the Times people. The idea is originated/created by one from a group of Japanese puzzlists including the grandmaster Tetsuya Nishio and the lovely lady Miyuki Misawa (perhaps tso could give the exact person)... It's a "baby" of 2 popular puzzles: sudoku/number place and kakuro/cross sums. In the latter the goal is to fill horizontal/vertical lines of digits to certain sums (just like a crossword) and you guess it right, a digit cannot be duplicated within each line. That keeps the max length of a line to be 9 and makes the considerations more simple/systematic.

Now if what I conjecture is right, when the Times borrowed the idea and renamed it from the unimaginative name of "sum number place" to the more catchy/funny/outrageous "killer sudoku", they must have some sort of agreement that the rules should stay in that way, in case there will be some sort of "international championships" among the Japs and Brits and all other people over the world. So as long as "killer sudoku=sum number place" numbers must not be repeated within cages. Even if this means you cannot have a cage larger than 9 cells.

If some smart a#@e wants to make it harder by allowing duplications within cages, they'll need to invent a new name for the puzzle, how about "murderer sudoku"? (I could see the "Times national murderer championship" could be more attractive than a "killer championship"...)

If somebody wants to see what a puzzle like that looks like, I heard that #91 of the Times "killer sudoku" book is one, by mistake or intentional. Having no access of the book whatsoever, I couldn't and wouldn't describe its details here or suggest anybody else to do it...
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Postby tso » Fri Oct 21, 2005 1:20 am

You are correct:

Miyuki Misawa's page is here.

The introduction says she designed it in 1994. Rules an solving hints are given as well.
Last edited by tso on Fri Oct 21, 2005 5:48 pm, edited 1 time in total.
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killer sudoku - repeat digits if a sum box overlaps a block

Postby steve » Fri Oct 21, 2005 10:45 am

I am constantly in awe at the speed of response from this forum - thanks to all and especially to udosuk for the excellent explanation. Now I can RIP. I realise that the better example of the limitation this rule creates is that you cannot have a sum box greater than 9 digits. As they say however "rules is rules"!
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