Rules of Sudoku

How to Solve Sudoku

Sudoku is a 9 by 9 grid that needs to be filled in with the numbers 1 through 9. The goal of sudoku is to place one number in each box so that each row, column and house have all of the numbers between 1 and 9 without repeating.

A typical Sudoku puzzle will start off looking like this:

  8 2
     
  3  
3 7  
     
    2
     
  5  
    7
  5  
  2  
  4  
     
  3 4
8    
8 9  
     
     
    1
     
    3
  4  
  2  
     
    3
    5
  1  

Before I get any farther I should probably start defining some terms. I've already used four in the first two sentances. If you've worked with sudoku before, you probably already know what I'm talking about, but then, you wouldn't be reading this section either.

Box:

A box is where you put a number. There are 81 boxes on a sudoku board.

Row:

A row is a horizontal group of 9 boxes. There are 9 rows on a sudoku board. They are numbered from top to bottom starting at 1. So, in the above example row 7 contains a 1, 4 and 3.

Column:

Much like a row, a column is a group of 9 boxes. However, they line up vertically. Columns are also numbered from 1 to 9 starting from the left. In the above example, column 2 contains 8, 3, 5, 2 and 4.

House:

A house is also a collection of 9 boxes and there are 9 houses on the board. The big difference from rows and columns is that each house is a 3 by 3 grid. The top three houses are 1, 2 and 3. The middle three houses are 4, 5 and 6. The bottom three houses are 7, 8 and 9. In the above example, house 4 contains 5, 2 and 4. These are the same 5, 2 and 4 from column 2. Odd houses have a white background and even houses have a gray background. This is simply to help differentiate the houses.

Every sudoku that is generated has exactly one solution. To learn how to solve the puzzles logically, look at the techniques section. By following these techniques (and really just the first two in the example above) the solution to this sudoku will look like this:

6 8 2
7 1 4
9 3 5
3 7 5
6 8 9
4 1 2
1 4 9
3 5 2
6 8 7
3 5 7
8 2 6
1 4 9
2 6 1
9 3 4
8 5 7
8 9 4
5 7 1
2 3 6
5 6 1
4 9 8
2 7 3
7 4 8
1 2 3
5 9 6
9 2 3
7 6 5
4 1 8