”Sudoku master, am I.” ~Yoda
Sudoku has taken the country by storm and many people want in on the fun. Before you decide to go out and get yourself a big book of Sudoku (or more precisely, before you decide to spend the next four days with whiteout and a bag of pens), an explanation of how to begin the puzzles is a must. Sudoku is the complete opposite of the Crossword. The Crossword is a game of addition while Sudoku is a game of elimination. In Sudoku, the most important part of completing a puzzle is the knowledge of what numbers can’t go where. This leads to a common practice in Suduko where the person writes the numbers that can go in a certain square off to the outside of the corresponding box and work the puzzle that way. While it works for some, it confuses me and it makes solving the puzzle much longer. As is with almost everything in life, keep it stupid simple- or, you know, something like that.
Let’s try and work through this Easy level puzzle that appeared in the Commercial Appeal on Monday September 25th. Below are going to be six different parts of solving a Sudoku puzzle. If all six ways are followed, any puzzle is solvable without getting ahead of yourself (which is a key with these puzzles). Some of the ways are obvious and some are a little more in-depth, but for those of you who want to start playing, these should help.
The lone rule of Suduko is- you must fill all the 3x3 squares and all of the columns and rows with the numbers 1-9 and none of the numbers can be duplicated in any of the squares, rows or columns.
(The red numbers are the numbers we’re filling in. Box refers to the entire 3x3 area. Squares are the individual squares in the box. The boxes/ rows/ columns are referred to as middle, low/ bottom, top.)
#1- The Obvious Fill
These are by far the easiest numbers to fill in. They are the way most people explain how to do Sudoku to beginners. In this case, all other 8 squares in the grid cannot be any other number because either that number is in the corresponding rows/ columns or there are other numbers blocking the squares. In this particular case, the number 1 cannot go anywhere else in this 3x3 grid because of the number 1’s in the other rows and columns make it have to go in the top right corner.
#2- The Sandwich
You’ll see this fairly frequently and it’s an easy way to start getting your numbers in order. When you have two rows/ columns finished for you, you know which three numbers can only go in those squares. In this case, we know where the numbers 1,4,6,7,8,9 are, so the middle row will be the numbers 2,3 & 5. In this case you see a 5 in the bottom right corner of the middle low box and a 5 in the middle of the top box. This makes the 5 go in the left square of the middle box. In harder puzzles, you won’t see your number as easily recognized, so look for a row/ column that has two of the numbers you need in it and the last number goes in that box. In this case, if in the middle low box, we took out the 8 and substituted in a 2, the number 3 would go in the middle square of the middle box and the 2 would go on the far right.
#3- Where It Can’t Go
This solving technique is not ordinarily needed in easier puzzles but in the hard one’s instead. In this puzzle, it’s used in its’ simplest form. To use this technique, a few conditions must be present. You must have three of a row/ column filled in a box. And, you must have a number in a different row/ column that is not in that box. In this case, before we filled in the 1, we had two empty squares in the middle row. Since there is a 1 in the top row of the top left box, there can’t be a 1 in the top row. Since there is a 1 in the middle of the middle right box, the 1 can’t go there also. So, after we’ve eliminated all of the other squares, the middle left square is where the 1 must go. Now, imagine (since this is much more common on the harder puzzles) that the 2 was not already in the middle right square. Where would the 1 go? It would go in the same place because the 1 must go in the right column in the bottom right box. You may not know what exact box the 1 should go in, but that’s for a later time. The fact that you know which row/ column it goes in is enough information at this point.
#4- By The Numbers
This is a solving technique that should be employed at every level of Sudoku. In the harder puzzles, many people forget the basics and try an intricate method of trying to solve the puzzle. Remember, a lot of the time, the easy way is, well, easier. Go through all of the numbers 1-9 and see which numbers you can get. Start with 1 and go through the entire puzzle, then 2, 3 and so on. After you go through the numbers, that box that was stumping you should start to become clearer. I have solved Sudoku puzzles by just employing this method by itself. In this case, finding one 8 led to finishing all of the 8’s in the puzzle. While this will not happen in harder puzzles, it will result in five to seven of the numbers being solved. Once you’ve taken some more of the squares out of play, you can start employing different strategies.
#5- The Column/ Row Approach
We are focusing on the bottom left square in the middle low box with the number 1 in it. Without the obvious way of solution, we have to resort to elimination again. On the bottom column there is a favorable situation that has arisen where we have four numbers filled in (4,5,8,9) and five numbers left to fill in on the column. Usually, this is not a good situation as you normally want to wait until you get six numbers in any row/ column to start to solve the row/ column in this fashion. But, with the 1 in the left low box, that means, 1 cannot be anywhere else in the box, so it must be in the middle low box. Now, since the 1 is in the middle row of the middle box, the 1 must be in the lower left square. There are a few different ways you can get this 1, but this way is a way you will use to solve harder puzzles that won’t be as obvious.
#6- Process of Elimination
The 9 in the middle row of the right middle box is another case of elimination. In this case, we can see that 9 cannot go in the bottom row because there is already a 9 in that row. Also, because there is a 9 in the top right square of the left low box, the 9 cannot go in that column either. Thusly, the 9 must go in the top row of the right middle box. Again, we don’t care that we can’t put the 9 in either one of those squares yet, we just need to eliminate where the 9 can’t go. So, since the 9 must be in the middle row and the far right column already has a 9 in it, we can put the 9 where it currently is. This is the reasoning you will need as the puzzles get harder during the week. Many times, the reasoning of that example can be twice as long in Expert level puzzles. In those cases, you will know which rows/ columns the numbers go in but not the exact squares. If you can keep reasoning things like this down as well as incorporate #4- By The Numbers, you can get through any Sudoku puzzle.
Here's what the puzzle looked like solved.
All right, we’ve started to get through this puzzle and ones like it. As the puzzles get harder, you going to need to employ many of these techniques at once to solve that one part of the Five Star puzzles that you will encounter. If you have any other Sudoku questions, just login and leave a post.
