Sudoku
in [Math]
|
Prev: How many Primes?
Next: divisor problem
From: mensanator@aol.compost on 17 Aug 2005 13:14 john_ramsden(a)sagitta-ps.com wrote: > m...(a)mimosa.csv.warwick.ac.uk () wrote: > > > > > Feel free to email me a superhard Sudoku to prove me wrong :-) > > > > To save me time, I wrote a simple program that fills in all > > straightforward deductions of the kind: > > > > 1) The only number that can go in this square is 3. > > > > 2) The only place where the 5 in row 7 can go is here. > > > > [...] > > Although it may sound almost heretical, I must admit these > Sudoko puzzles leave me completely cold; they seem almost > as daft and pointless as those alphametic puzzles such as > CAT + DOG = SCRAP. Personally, I find the journey more interesting than the destination. I gravitate towards the puzzles that lend themselves to computer solving because that's what I'm interested in. > > (That's not meant to imply I find either type easy, quite > the reverse.) And many problems that can be solved by brute force are intractable on practical computers. So you have to be clever, and _that's_ what I enjoy. > > But, changing the topic temporarily, I did used to enjoy > the Rubik's cube, and I wonder if anyone has yet found a > workable and neat way to represent all the patterns and > operations in a group theoretic form or something similar.
From: Axel Vogt on 17 Aug 2005 14:25 Ioannis wrote: > > Ï "Stephen J. Herschkorn" <sjherschko(a)netscape.net> Ýãñáøå óôï ìÞíõìá > news:0lpMe.941$EZ5.81(a)fe08.lga... > > > > Here is another benefit of doing sudokus on an Excel spreadsheet. The > > Edit/Undo command keeps a buffer of significant length, so if you find > > you made a mistake, you can undo the last ten or so changes. > > Thanks to both Stephen and Paul for their help. Oughta keep my uncle busy > for quite some time :-) may be you are interested in a Maple solution, then check that link: http://beta.mapleprimes.com/blog/joe_riel/solving_a_sudoku_puzzle_with_maple
From: Puppet_Sock on 17 Aug 2005 15:03 Stephen J. Herschkorn wrote: [complicated colour scheme for doing Sudoku in Excel] I do use Excel for the more difficult puzzles. But I've never found such colour schemes to be particularly useful. First, save the original matrix by just doing copy/paste. If you've set column widths to make things more attractive, just paste the saved image down a bunch of rows. I've sometimes found bolding the cells with exactly one number determined to be useful. But that's about as far as I've wanted to go. Occasionally if I'm trying to use "guessing" I will copy the matrix as far as I know it, then turn off all bolding, then bold the cell I'm guessing in. So far, however, I've not found a puzzle that I needed guessing to solve. When working the puzzle, I usually just find that highlighting rows/cols is all the functionality I need from Excel. For example, highlight all the rows and columns you know have a 1 in them. You can do this by clicking the first one, then holding the control key down to click the others, so they all highlight. It works best if you leave the puzzle one row and one column away from the edge of the worksheet. This leaves the cells over that you don't know about, and makes it visually obvious where to consider putting a 1. If it's a very difficult puzzle, I may need to type into the other cells the values they could be. Then you can spot things like "there is only one cell in that 3x3 block that contains a 7, even though I have not eliminated all the other values from that cell yet. So it must be a 7." Socks
From: r.e.s. on 17 Aug 2005 15:06 "John R Jones" <a1jrj(a)hotmail.com> wrote ... > I then wrote a macro to copy the musts to the puzzle cells, > re-apply the algorithms and iterate until there are no more > musts. > The idea was that I would then only have to guess some values > and backtrack manually. > However, I have yet to find a puzzle that isnt automatically > filled in by the blessed thing :-(. > Any really tough ones out there? Try it on this one: . . . | . 7 . | 3 . . 5 . . | . 1 . | . . 6 . 9 . | . . 2 | . . . ---------------------- 8 . . | . . 5 | . 9 . . . . | . 4 . | . . . . 2 . | 1 . . | . . 7 ---------------------- . . . | 9 . . | . 8 . 4 . . | . 6 . | . . 3 . . 7 | . 3 . | . . . --r.e.s.
From: Bob Jordan on 17 Aug 2005 21:08
Stephen J. Herschkorn wrote: [complicated colour scheme for doing Sudoku in Excel] I find the Excel conditional formatting concept the most useful. I have one region to type in the original definition of the problem and then below it a working region. After clearing the initial region I type in the numbers for the original problem. I then copy that whole area and paste it into the working region below. Previously in the working region I set up a conditional formatting for all 81 squares which sets the square to red if its value matches the value of the corresponding cell in the input region. I can then type in new values which show up as black so I can see which are my work and which are original which show as red. As a variation of this if I come to a point where I may need to investigate two or more branches, I copy my current state back up to the original definition area (you have to be sure you are right to this point though). Now all the currently filled squares go red and I can work down one of the branches with all steps showing as black against red for all numbers that I think are definitely OK. If I get to a dead end I can delete one by one all black squares and try the other branch. In reality I have lots of aids floating around all the lower regions of the spreadsheet which I can choose to use to help. This I use particularly when investigating paths. It is most interesting to calculate the number of possible moves ahead at each point in time and from this you can see how much different the easy and Fiendish puzzles are. But thats another story. Yes a wonderful puzzle which Excel has helped me to understand. But mostly I enjoy doing them with pen an paper. My method is to write small numbers on lines or corners to show the only places a number can go. So if I determine that a 5 must go in one of two adjacent squares I draw a 5 on the line between them. Similarly if it must go in one of 3 or 4 adjacent squares i draw it on the corner. Then later when some of those squares are filled I may be able to fill in the others without thinking further. Later I may start to write in the lower part of a square ALL the possible numbers for that square. Similarly if a number can go in two or three non-adjacent squares I write those numbers in small numbers at the top of the square. It is all a bit of a mess but - hey I love it. |