Notes and musings on Sudoku
including a spreadsheet to do the mindless labor

Some quick jumps:
Just give me the spreadsheet, please
The book The Sudoku Code

I assume that anyone coming here already knows the basic rules of Sudoku. If not, take a look at its Wikipedia entry for a good explanation.

Basically, given a 9 X 9 grid of “entries”, partially filled in with the integers 1 through 9, the objective is to fill in all the remaining entries such that the integers 1 through 9 appear exactly once in every row, column, and heavily outlined 3 X 3 “box”.

One way to systematically solve Sudoku puzzles is to put a “Possibility List” into each entry in the grid, which initially contains all the integers 1 through 9. Then, whenever a number is put into an entry, that number can be struck out of the Possibility List everywhere in that entry's row, column, and box. Usually, either some entry's Possibility List gets reduced to a single number, or a given Possibility can be found in only a single entry in a row, column, or box. At that point, the entry can be set. Sometimes, on particularly difficult problems, you need to make a guess, and then do some backtracking if the guess turns out to be wrong. The spreadsheet also helps with that.

The spreadsheet

I've made an Excel spreadsheet to do this mindless work for you! You may freely download this spreadsheet by going to the following page. WARNING! The spreadsheet makes it so easy to solve Sudoku puzzles that you may no longer find them interesting!

Sudoku is not an arithmetic puzzle

I'm constantly amazed by the number of writers who describe Sudoku as an arithmetic puzzle, just because it has numbers in it. The fact that the integers 1 through 9 are used in Sudoku is entirely incidental. Sudoku could just as easily been defined by saying, "Fill in the 9 X 9 grid such that each row, column, and 3 X 3 box contains each of the letters A through I exactly once." Or nine arbitrary symbols could have been used: a smiley face, a heart, and so on. The fact that numbers were used is entirely incidental.

While it's not an arithmetic puzzle, it is most certainly a logical puzzle.

Sudoku puzzles certainly have to be created carefully, probably with the aid of a computer. A grid that is partially filled in could easily have no possible solutions, one solution, or multiple solutions. A proper Sudoku puzzle must be carefully designed to have exactly one solution.

Sudoku puzzle transformations

How many different Sudoku solutions are there? Lots! but perhaps fewer than you think.

Click here to read about how to transform a Sudoku solution into a whole collection of solutions - up to 4,875,992,432,640 of them! There's even another spreadsheet to play with, although it doesn't help you solve any puzzles.

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This page was last updated November 30, 2006