Introduction to Sudoku

All of the red words in this article are dynamic. Click on them to get helpful clues!

New to Sudoku? Still can't remember whether it's spelled "Sudoku", "Soduko", or even "Barbeque"? Still think Sudoku is a counting game or has something to do with math? Then this is where you should start.

First, let's get the pronunciation out of the way. The trick to remembering how to pronounce Sudoku is to find a mnemonic. Try thinking of the word "psuedo" and then attaching "ku" to the end. Or if that doesn't work, you can just get it tattooed on your stomach.

Now that we know how to pronounce it, just what the heck is it? Sudoku is a simple game that can be very difficult to master. The object of the game is to use logic to deduce the missing pieces of the puzzle. Sounds simple enough, right? Yes, Sudoku is deceptively simple at first sight. However, extremely difficult Sudoku puzzles can take hours to solve, even for advanced users. Don't let that scare you, though. There are puzzles for every stage user, whether a complete beginner or very advanced.

In Sudoku there is a grid, usually 9x9, that is only partially filled with numbers. The object of the game is to fill in the empty spaces, called cells, in such a way that no number appears in a unit twice. Rows, columns, and boxes are all units. Don't worry if your mind wandered when you read that. I will give plenty of examples. But first I'll state it another way: there is only one possible number that can be in each cell, and your job is to figure out which one. You simply need to remember that every row, column and box must not contain the same number twice. That is it.

To help make this concept clear, let's look at an example. To your left you will see a small 4x4 Sudoku puzzle. 4x4 puzzles are usually too small to provide much of a challenge, but they are great for the complete beginner. In this puzzle you will see that there are two bold lines splitting up the puzzle into quadrants. Each of those quadrants is called a box. A 4x4 puzzle will have 4 boxes, and a 9x9 puzzle will have 9 boxes, and so forth. Go ahead and take a look at the puzzle for a few seconds and then click on this to see what the solution is.

Looking at the solution we see three things: Every row, column, and box have all of the numbers 1, 2, 3, and 4 in them. There isn't a single row, column, or box that has a number repeated. For example, if you find that a row in your puzzle has the number 3 in it twice, then you know something is wrong.

Once you feel you've gotten a fairly clear grasp of the concept, you can click here to clear the solution and try to solve it on your own. Well, not completely on your own... I'm here to help.

To start off we'll focus on the first row. At the moment there is only a 3 filled in, and from this we can logically infer that the other cells in the row must contain 1, 2, and 4. But where do they go? We know that the number 4 cannot go into the first cell because there is already a 4 in that column. Likewise, it can't go into the last cell because there is already a 4 in the last column. That leaves only one cell in the first row that the number 4 could possibly go in: the second cell. Here is what the puzzle looks like after filling in the 4:

Now let's move onto the second row. 3 and 4 have already been filled in for us, so that leaves just 1 and 2. We see that the number 2 can go in the first empty cell, but not in the second empty cell because there is already a 2 in that column. Therefore 2 can only go in the first empty cell. Click here to update the puzzle with the number 2. Now we only have the number 1 left for the second row. It should be pretty obvious where it goes. But if you are still unsure, click here to see. Likewise, the third row only has one empty cell left with 1 as the only one possibility.

Now most of the puzzle is complete. We only have the corners left to solve. At first this may appear tricky because they all depend on each other. Each corner must either contain a 1 or a 2. If one corner contains a 1 then the two corners adjacent to it must contain the number 2, and vice versa. So which is which? To solve the puzzle you must remember that not only are columns and rows considered units, but boxes are also units. Let's focus on the top left box first (click here to highlight it). We see that the box already contains the number 2. Therefore the empty cell in the top left corner cannot contain a 2, and so must contain a 1. We can now solve the rest of the puzzle.

You have now seen Sudoku in a nutshell. But don't assume that Sudoku is just a matter of scanning a grid of numbers. We have utilized here the two easiest techniques for solving a Sudoku puzzle: Single Position and Single Candidate, and indeed the easiest Sudoku puzzles may only require these two techniques. But any puzzle of medium difficulty and higher will require deeper analysis. There are all kinds of advanced techniques with fancy names like X-Wings and Remote Pairs that are required in some of the tougher puzzles. But make no mistake. These are not tricks. There is no magic in Sudoku; only reason and logic.

A common misconception about Sudoku is that it is a math game. No math is needed to solve Sudoku, only logic. And before you rush to send me an email telling me that Logic is in the domain of Mathematics, let me set the record straight and say that Mathematics does not hold a monopoly on logic. Indeed it is the other way around. Logic gave birth to Mathematics. It is not possible to say the opposite.

Besides, Sudoku does not really have anything to do with numbers. Although it is true that most Sudoku games use numbers, there is no rule stating that Sudoku must be this way. Any symbols will work, such as letters, heiroglyphs, or pictures of babies doing the mashed potato. It doesn't really matter. The only thing that matters is that each row, column, and box do not have the same symbol twice. Also, sudoku puzzles do not need to be 4x4 or 9x9, or even square for that matter. Really there are more variations of Sudoku than you could shake your pen at. Why, you ask? Just play a game or two and you will see exactly why: Sudoku is almost as addictive as crack cocaine. But much safer, of course. And cheaper.

Now that you understand what Sudoku is, it's time to learn about some of the techniques you have available to solve them. Click here to read about the Single Position technique, the starting point for all Sudoku players.