Quote:
Originally Posted by shabbir
tailhook123, Nice sheet but you tend to not come to the solution in this manner.
Its not meant as a one button solution. I thought it interesting and was something I built as a visual helper for solving sudoku's. I've done the hardest of the hard sudoku's with it. The further permutations were a bit much for a spreadsheet. Once you have the lower right:

1) check to see if any cells only had one solution. Carry that up to the upper left and enter it.
2) go by row and column and check to see if a number appears only once.. if it does.. that cell is that number.
3) go by cell block and see if a number appears only once.. if it does.. that cell is that number.
4) if a number in a cell block appears in only one row OR one column of a cell block... remove that number as a possibility from that row or column in any other cell block.
5) if a number in a row appears in only one cell block.. remove that number as a possibility from the other two rows in that cell block.
6) if a number in a column appears in only one cell block.. remove that number as a possibility from the other two columns in that cell block.

I've done up through hard with those 6. If you hit a wall(usually 'evil' puzzles) you have to do selective solutioning. What that means is you find a cell for which there are 2 possibilities. You preferably want one for which if you choose a specific one of the two numbers... another cell will solve. When that happens the grid will start to collapse under the 6 passes above and it will typically either solve or break. A break is when you picked the wrong one of the two options. When this happens you will get a cell with no possibilities and in turn prove the other option in the original 50/50 cell was correct.

The lower right grid makes solving these things much, MUCH easier. People doing this just without help do variations on that grid with dots and whatever to keep track of possibilities.