Sunday Sudoku

When I first started solving Sudoku puzzles, I used a "brute force" approach. I wrote tiny numbers in every square for every possible value that square could have. Invariably, I would find one or two squares that could only have a single value (e.g. last row, fourth cell from the left can only be a 2).

This discovery would cause me to go back and eliminate all the 2's from that same column and row, which would usually give me another cell that could only be a single value. The process tends to sustain itself, as you can see. It's actually a successful strategy, but it's labor intensive, tedious and takes up a lot of time. Who wants to spend an hour a day or more working sudoku puzzles?

So, you begin to find other tricks (from trial and error, or talking with other people who do sudoku puzzles, or reading books on the subject) that cut down on the time and effort. For example, I can see that the value of the fourth column, fourth row has to be a 1 because the 1's in the fifth and sixth rows make it impossible for any other cell in the middle square to have a value of 1. Since each square has to contain one cell with the value of 1, the process of elimination makes it necessary for the fourth column, fourth row cell to be 1.

Likewise, the 9 in the sixth column makes it impossible for the two cells above it to have a value of 9. The only cell left is the fourth column, fifth row. The only two numbers remaining for the center square are 3 and 6, and the 6 in the sixth row makes that pretty obvious. See, we've solved the entire center square and I didn't have to write down each possible value for the four empty cells in order to do it. There's something to be said for techniques that save time and effort.

I must admit I do still revert back to the "brute force" approach when faced with puzzles of great difficulty. I suspect there are probably other tricks and techniques out there that I am not yet aware of. If I could add a few more of those to my proverbial toolkit, I'd probably be faster/more proficient at solving these harder puzzles.