Stumped in Sudoku
February 28, 2005 9:54 PM Subscribe
I'm having a lot of trouble finding a logical solution to a Sudoku problem.
posted by obiwanwasabi to Sports, Hobbies, & Recreation (13 answers total)
The problem was published in The Times on 18 February 2005 with a rating of "fiendish". I have an Excel spreadsheet that solves Sudoku puzzles by brute force, and it confirms that the puzzle can be solved (albeit with a "very hard" rating of 8).
The puzzle is crudely reproduced below. Bold numbers are the original starting numbers; the rest are numbers I've solved. The Excel Sudoku solver confirms that the numbers I've placed thus far are in their proper positions.
I've reached the stage where I cannot logically deduce the positions of any other numbers. I've never had to guess to solve a Sudoku puzzle before - with a little thought, I can state with certainty that a particular number can only be placed in a particular position, and that therefore this number goes here, and that number goes there, and so on til the grid is solved. The Times claims that their Sudoku puzzles are constructed so that guessing is never required.
I'm not looking for a solution to the puzzle - I know what it is already. I'm hoping that somebody can say something like "well, given that C5 is a '3', and given that G6 is a '9', it follows that D1 must be a ..., because ...". Just one number to get me going would be lovely. A new solving technique I hadn't thought of would be brilliant.
For those not in the know, the challenge is to place numbers in the grid such that each row, each column and each 3x3 square contains the numbers 1 to 9.
_ 1 _ | _ 6 _ | _ _ _
5 8 9 | 7 3 4 | 6 2 1
_ _ 6 | 1 _ _ | _ _ _
8 9 7 | _ 1 6 | _ _ _
_ _ 3 | 8 4 7 | 9 1 _
_ _ _ | _ _ 3 | 8 7 6
_ _ _ | _ 7 9 | 1 6 _
_ 3 _ | 6 2 5 | 4 _ 7
_ _ _ | _ 8 1 | _ 5 _