Sudoku

An Excel Solver

I created an Excel spreadsheet that solves any Sudoku puzzle.  Most are solved strictly with simple strategies, such as hidden and naked singles, doubles and triples, and a number in two or three cells that intersect in both a row, column or box and another row, column or box.  If necessary, it employs a more advanced process that finds patterns known as wings, chains, fish, and coloring.  For more information about advanced strategies, see note below.

By setting the speed, you can watch the program solve the puzzle cell by cell.  There is also a library of more than 200 puzzles borrowed from various sources on the web.

Updated 8/27/2007: V2.15 now available - minor bug fix to prior version.

Right click here and select "Save Link As" to download this spreadsheet to your computer.

If you have any comments or suggestions, email me at andy@bangser.com.

Advanced Strategies

The solver employs two advanced strategies that are (subject to confirmation) equivalent to forcing chains, X-Wings and other strategies found on many interesting web sites.  They are:

1. Evaluate the candidates in a cell (using basic strategies) and evaluate any that lead to a "dead end".  A dead end is reached when any cell on the board is left with no remaining candidates, or when any row, column or box is left with no candidates for any particular number.

2. For candidates that do not lead to dead ends, determine whether their outcomes unanimously agree that any candidates in other cells are not in the solution, and so turn those other candidates off.

When this solver is set to "No guessing", it will not stop when evaluating candidates if they happen to lead to an 81-cell solution.  Those solutions will be ignored and the program will continue to evaluate candidates as above.