ECOURSE PART 3: BEGINNING THE CHALLENGE

Below is an unsolved Sudoku puzzle. It consists of a 9 x 9 grid that has been subdivided into 9 smaller grids of 3 x 3 squares. Each puzzle has a logical and a unique solution. To solve the puzzle, each row, column, and box must contain each of the numbers 1 to 9. Throughout this guide the entire puzzle will be referred to the “grid”, a small 3 x 3 grid as a “region”, and the square that contains the number as the “cell”.

Rows and columns are referred to with row number first, followed by the column number:

4,5 is row 4, column 5

2,8 is row 2, column 8

Boxes are numbered 1 – 9 in reading order: 123 456 789

Guessing

Try not to guess. Until you have progressed to the touch and diabolical puzzles, guessing is not only totally unnecessary, but will lead you up paths that can make the puzzle virtually unsolvable. Simple logic is all that is required for gentle and moderate puzzles. Most puzzles that are rated easy to hard will require some sort of analysis.

Starting the Game

To solve Sudoku puzzles you will need to use logic. You need to ask yourself questions like “if a 1 is in this cell, will it go in this column?” or “if a 9 is already in this row, can a 9 go in this cell?” To make a start, look at each of the regions in the grid below and see which cells are empty, at the same time checking that cell’s column and row for a missing number. In this example, look at region 9. There is no 8 in the region, but there is an 8 in column 7 and in column 8. The only place for an 8 is in column 9, and in this box the only cell available is in row 9. So put an 8 in that cell. Once you have done this you have solved your first number.

Next time we'll be discussing alittle about "Searching for the lone number".