![]() And for the square at 7,8, any of the numbers will work: For the square at 7,6, we can pencil in a 5 and a 6. Using the same process for the square at 7,5, we can eliminate the 4 and the 9 (box 8 already has one of each) and pencil in a 5 and a 6. So we're going to pencil in "5 9" for the square: The 9 could go there, because row 2 and box 7 are both missing a 9. The 6 is out because box 7 has a 6 already. The 5 is a possibility, because neither row 2 nor box 7 has a 5 yet. So, of the numbers 4, 5, 6 and 9, which could possibly solve the square at 7,2? The 4 can't go there, because column 2 already has a 4. We're going to pencil in all of the numbers that could possibly solve each empty square, respectively. There are strategies we can use when the solution is not so obvious, and it all starts with some little pencil marks. ![]() Since this is an easy puzzle, we could probably solve a good portion of it this way. We've now solved all of column 4, and we used only simple logic to do it. So right there we know the 2 goes at 5,4, and the 7 must go at 7,4: Since box 5 already has its 7, we can't put a 7 in the 5,4 square. The empty square at 5,4 interacts with row 5 and box 5, and the empty square at 7,4 interacts with row 7 and box 8. Now let's solve the rest of column 4, which still needs its 2 and its 7. Neither row 3 nor box 2 already has a 6, so we know the 6 is correct for that cell. Can the 7 go there? Row 3 already has its 7, so we can't put a 7 there, either. The " simple logic" approach to sudoku requires only visual analysis and goes something like this: Can the 2 go in the empty square? It can't, because box 2 already has a 2, and it can only have one of each number. To fill the empty square at row 3, column 4, we're going to have to look at column 4, row 3 and box 2. Take a look at the empty square at row 3, column 4 (3,4), and the row and box that interact with it: So where does each number go? To find out, we need to look at the rows and boxes that interact with column 4. But we can't just put them anywhere - each number has a specific location in the puzzle's answer. In order to have one and only one of each digit from 1 to 9, we're going to have to provide column 4 with its 2, its 6 and its 7. If you can solve an easy puzzle, you can solve a hard one - it'll just take you more time. Let's walk our way through the easy puzzle above to get a feel for the process. The best way to learn the art of sudoku is by working through a puzzle. (Michael Mepham, puzzle creator for London's Daily Telegraph, rates his puzzles as either Gentle, Moderate, Tough or Diabolical.) An easy puzzle gives you enough numbers placed in enough strategic positions to allow you to find the answer using fairly simple logic. Sudoku has several levels of difficulty, from easy to very hard, based on how many numbers you get to start with and where those numbers are positioned. ![]() Here's an example of a real sudoku puzzle from Michael Mepham's "Book of Sudoku 3":Ī sudoku puzzle has some "clues" filled in. ![]() A sudoku puzzle already has some of the numbers filled in, and it's your job to figure out where the rest of the numbers go. Of course, starting with a blank grid wouldn't make it much of a challenge. So if you were to start with a blank grid and fill in the numbers for row 1, column 2 and box 4 according to the sudoku rules, it might look something like this: It's the interaction between the rows, columns and boxes that tells you where the numbers need to go. The goal of sudoku is to fill each nine-square row, each nine-square column and each nine-square box with the numbers 1 through 9, with each number used once and only once in each section.
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