Sudoku: How to Play
Not sure how to play Sudoku? Then follow this guide which will teach you the basic principles in playing the game.
The first thing that you should do, is pick a place to start on - usually the box with the most numbers already in it is a good place to start, so for this example, we will be concentrating on the bottom left box. The aim of the game is to insert the numbers 1 to 9, in every 3x3 box, every row, and every column - so you can only use each number once.
The first thing to do is to see which numbers are already missing from the 3x3 box, so for our example, the numbers 4, 5, 7 and 9 are missing. You can start by trying to solve from any of these numbers, for simplicity, we shall start by looking for the number 4's position within the 3x3 grid (left). The number 4 cannot go within the same row, or column as an existing number 4. The blow grid shows where the number 4 cannot go within our grid, because of a 4 located in the same row where we could place a 4. However, we also notice that we can place 4's in the boxes that are left over, so we write a small number 4 in the corner to remind us that we could place this number here (as it can go in 3 places at the moment - we cannot finalise its position).
The next number to look at will be the number 5, as before with the number 4, we ignore the positions where the number 5 cannot go (as it cannot go in the same column or row as another 5). This time (see below), instead of having more than one place to put our number 5 in, there is only one blank space - so we write a big number 5 in this box, as it is the only place it can go.
We now will demonstrate where the number 9 will go. Like with the numbers 4 and 5, we ignore the rows and columns where an existing number 9 lies, and we place our little number 9's in the corners of the boxes where it could go. From the below example, the number 9 can go in all 3 of the existing blank boxes - this means that perhaps the number 7 will reveal the location of where both of these numbers will go.
The last number we need to look at is the number 7, hopefully this will show we will be able to place the numbers 4 and 9. As we have done previously, we ignore the rows and columns that existing 7's lie in. We then realise that there is only one possible location for this number to go into - so we write a large 7 in this box.
Now we know where the number 7 goes, we can decide where to put the numbers 4 and 9. As the number 9 is the only number in the bottom blank square, we insert this there. We always wait to see if any other numbers can go into this box at the end, just in case we incorrectly guess where it goes. This now leaves the number 4 to go into the top right blank box.
Now we have completed this 3x3 square, you can now carry on and complete the entire grid, using the same basic principles. Usually it is best to do the next grid to the one you have just completed, or the on adjacent to that. After you have completed a few of the easy sudoku puzzles, you will get quicker in completing them.