Solving Sudoku puzzles the Wise way

My wife and I had both been curious about sudoku puzzles so when we were flying to the east coast I took an enlarged copy of a easy sudoku puzzle to work. We found that was something we enjoyed doing together. In fact it reminded me of my grandparents and later my parents working the crossword puzzle together. I’m sure it was one of the things they looked forward to everyday. Personally I don’t like cross word puzzles - probably because of my poor spelling.

My wife and I then bought a Sudoku puzzles book and we were off solving puzzles. One of the first things we discovered was you need a much larger grid to work the puzzle on. At first we just drew one in a notebook but that got old pretty quick. I went to an Office Depot and drew up a 9 X 9 grid with the 9 boxes outlined in thicker ink. I then had them run off a 100 copies. Later I used my grid to have Sudoku pads made up. Now all you need is a puzzle to work. We’ve found Sudoku puzzles everywhere, newspapers, magazines and books full of puzzles. They are generally rated by difficulty from easy to unsolvable. We’ve found that it’s best to have the answer available before you start the puzzle. When you first start out you may want to check and see if you’re on the right track by checking the answers.  I know we did. There’s nothing worse than working most of a puzzle and finding you’ve made a mistake.

Once you’ve selected a puzzle to work, copy it to the pad. We found it helped to write the puzzle number on the pad too. I suggest that you work the following puzzle with us. The rules for a puzzle are:

• There are 9 rows, 9 columns, and 9 boxes.
• Each box, each row and each column must contain the numbers 1 through 9.

That’s it.

Each puzzle gives you numbers to work with and your job is to figure out the missing numbers. We would like to give you some pointers on how to do that. First, some navigation tools. We’ll number the columns across the top from left to right 1 to 9 and the rows from top to bottom 1 to 9 and the boxes from top to bottom left to right 1 to 9.   Squares will be displayed as (column, row) throughout this training. We’ll use these numbers to point out a clue to finding a number.

Using the example of the puzzle above let’s track down the easy ones. First we start with all the squares with the number 1. Check the other columns and rows to see if we can find a place where only that number can be located. In our example, we progress to the number 5 before we find what I call a “freebee”.  We have a 5 in (3, 1) - that’s column 3 row 1. We also have a 5 in (5, 2). This means that we can only have a 5 in box 3 row 3. We also have a 5 in (8, 9) leaving the only place a 5 can be is (9,3). We can now look at box 6 and see that the only place a 5 can go is (7, 5). As often happens this leads us to another 5 at (1, 4). At this point we only have one 5 left to find in box 8 . If you eliminate the 5’s in columns 5 and 6 and the 5’s in rows 8 and 9 the only place a 5 can be is (4,7). I have put in the 5’s and circled them with a number showing the order I found them.

Another process we do is to identify places where there are 2 squares where a number can go. If you look at box 9 you will see that the only place a 2 can go is (8, 7) and (9,7). We write a small 2 in the bottom of those boxes so if one of the boxes gets filled in we know that the other box must be a 2. A note about small numbers in the bottom of the box: we’ve found that putting them in ascending order left to right is helpful. This is what the puzzle looks like after phase one (finding the freebees).

Next we look for columns, rows and boxes that have the fewest open squares. In this puzzle column 7 only has 2 open squares so we’ll start there. Determine which numbers are missing and write them at the bottom of the column. In this case we’re missing the 2 and the 6. Go to square (7,2) our first open square and see if either of the missing numbers are in box 3 or row 2. It turns out 6 is in both box 3 and row 2. This means that 2 has to go into square (7,2). It also means that 6 is the only number left to go into square (7,8). We now have column 7 completed.  Next, let’s do box 3 since it only has 2 open squares. Here we put a circled one to show the top box and list the missing numbers. The missing numbers are 1 and 4 and we list them beside the circled one. We find that we have a 4 in row 3. That means 1 must go into square (8,3) leaving the 4 to go into square (9,2). This is what the puzzle should look like now.

Now let’s fill in box 9 . Circle a three below the circled 1 leaving room for a circled 2. The missing numbers are 1, 2 and 9. Lets look at square (8,7) and we see that column 8 has a 1 in it. Now we know that the only numbers that can be in square (8,7) are 2 and 9 so we’ll write a small 2 and 9 in the bottom of that square. Once we’ve determined the only possible numbers that can be in a square we place a dot in the upper right corner of the square indicating those are the only number to look for. Next we look at square (9,7) and see that all the numbers can still be used there so we put a small 1, 2, 9 and put a dot in the square. The last open square is (9,8) and we find a 2 in row 8 leaving only 1 and 9 for that square. Puzzle with box 9 missing numbers identified I’ve continued working the puzzle and have come to row 3. When I worked box 1 I only had 2 open squares and they both contained 2 and 8. Any time you only have the same 2 numbers occupying 2 squares in a box, column or row it’s called a matched pair and you can exclude those number from the rest of the box, column or row. So we have a matched pair 2 and 8 in box 1 and in row 3. This means we eliminate 2 and 8 from the rest of row 3. Example of matched pair.

Continue filling in all the blank squares by box, column and row until they are all filled in with either the number or small numbers in the bottom of the square. While filling out row 1 I came across a lone number. That means that the number 2 only shows up in one square (4,1). When this happens you know that’s where it has to go.

When you do box 7 you should find another lone number. In box 6 you should find another matched pair. When you find a number look around and scratch it from the other squares in the box, column and row. Often you will find it starts a chain reaction of finding numbers. This is the completed puzzle.

At this point you should be able to work most easy puzzles. Later we’ll go into some more advanced stuff.

Here is a blank work sheet. If you put your mouse over it and right click you should be able to "save picture as" then print the saved picture. Good Luck.

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