5 Star Sudoku Solving Simplified

by Dave Peck

Sudoku puzzles, they are catching on! Everyone is doing them. Here's how to get into the game. It may seem difficult at first, but more than strictly intelligence, success at Sudoku is a result of understanding relationships and teaching yourself how to spot them.

Sudokus are number puzzles made up of 81 squares divided into nine blocks. The object of the puzzle is to fill in all of the squares so that each row has numbers 1-9, each column has numbers 1-9, and each block has numbers 1-9 with no repeats. The puzzle promotes deductive reasoning. If your guessing, then you're really not accomplishing anything. The key to solving a Sudoku puzzle is by viewing each row, column, and block as independent groups that effect each other as they are all connected. There maybe more than one route to solving a puzzle, but no matter how it is solved, there is only one solution. Notes are encouraged around the outside of the puzzle, but you should not have to be writing notes inside the puzzle making it harder to look at.

The methodology of solving Sudoku is not that hard. Mostly it relies on observation and is based on these methods.

Naming Conventions
For the purpose of this tutorial, I'm naming rows, columns, and blocks as follows:
Rows: 9 rows, named 1-9 from top to bottom
Columns: 9 columns, named 1-9 from left to right.
Blocks are groups of 9 squares named from top left to right 1,2,3, to middle blocks 4,5,6, to bottom blocks 7,8,9.
Squares hold individual numbers.

Disclaimer
I am not an expert on Sudoku, just knowing enough to be dangerous. The purpose of this tutorial is to familiarize you with some techniques to solve a 5 star puzzle. In actuality the same methods are used for all Sudoku puzzles regardless of how difficult they are.

Links
Sudoku Dashboard Widget - for MacOS 10.4.
Sudoku Companion
USA Today Daily Sudoku
Web Sudoku
Sudoku.com

The following is borrowed from an older USA Today 5 star puzzle (solution all ready published) with lots of empty squares. This is not the most difficult example of a 5 star puzzle. More difficult puzzles may be posted in a future edition.

First off save this puzzle to your computer and print it for practice. (Right click on puzzle and select "save to disk".

1. First lets look for some freebees.	2. Remember each number (1-9) can occur in each row, column, and block only one time. By looking at 1s in columns and rows and comparing them to blocks, we can determine where these 1s go.	3. Easy start.
4. The three blocks in the middle are the strong areas of the puzzle because they have completed sections. I am going to be looking at these rows and adjacent blocks.	5. I'll start by comparing block seven (1,2,3) with row seven (1,8,7,6). Because 2 and 3 are all ready located in block seven, they can't be repeated in the intersecting portion of row seven. Therefore they must be located to the far right and fortunately there are only 2 open squares there.	6. We've determined that 2 and 3 must be located in the far right side of row seven. And because there is a 3 in column seven, the 3 in row seven is placed as shown.
7. That leaves only one spot for the number 2 in row seven.	8. Now look at row seven again. The missing numbers are 4,5,9. But a quick look at column two reveals that 5 and 9 are all ready displayed, therefore, 5 & 9 could not be repeated at the intersection of row seven and column two. Only the 4 can go there.	9. Current progress.
10. Now compare column nine with block nine.	11. In block nine, the missing numbers are 7,8, and 9. But because 9 is all ready located in column nine and can't be repeated in the portion of block nine that intersects with column 9, you can see that 9 has to go on the left side of block nine.	12. Current progress.
13. Here is an example for lack of a better term, a Pseudo number where the exact location of a number is unknown, but knowing what row/column it's in can help you deduce where a number is in another block.	14. Looking at block seven you can deduce that 8 must be in the center column, but it can go in either of the open spaces.	15. Using this info, you can deduce where the 8 is in block one.
15. It's worth showing but unfortunately the example in this puzzle does not help nail a location for number 8 in block one. If there had been an 8 in rows one or two, this method would have helped place the 8 in block one.	16. The next number I'm going to place is a 9 in row five. Look at the puzzle and see if you can spot it. Hint is in next frame.	17. Here is the row and the block. I'm also going to use the 9 in two other columns to place the 9 in row five.
18. The solution.	19. After completing this 9, I look around and try to see if it helps me with any other block, row or column- not yet. But I just spotted a 7 I can place. Take a look. Hint: There are only two 7's on the puzzle so what do they have in common?	20. Answer: I can determine the location of 7 in block seven.
21. Ok here is the perfect example for looking around after placing a number to see if it helps somewhere else. Do you see it?	22. Block nine only has two numbers left to fill, the 7 and 8. What does this seven tell you about block nine?	23. Now you know how they go. Place a 7 and 8 in block nine. Do they help anywhere else? You betcha. Hint: Look to place another 8.
24. Over in block seven, the 8 can be placed.	25. Take another look at block seven. There are only 3 numbers left to fill in- 5,6,9. How do I know by looking at column two where the 6 goes? Answer: There is a 5 and 9 all ready in column two so the 6 must go at the bottom of column two. In addition there is a 6 in row three and one in row six precluding the placement of a 6 in any other position other then the bottom of column two.	26. Column two only has two missing numbers left- 2 and 3. What cha think? Answer: There's a 2 in row three so the 2 in column two must go at the bottom open square.
27. Column two complete. Now look at row three. I'm using a block and a column to place a 4 in row three. Row three is missing four numbers- 4,5,7,8. How can I deduce where the 5,7, and 8 don't go?	28. This might not look clear, but there is a 5 and 7 in block one and there is an 8 in column three. So of the four numbers left in row three, which one can go in the bottom right corner of block one?	29. Answer: The number 4! Lets continue with row three. Tell me where the 5 goes? Hint: 5,7, 8 are the three missing numbers. What numbers are in column nine?

Continue to Sudoku 5 Star Tutorial Part 2 ->

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