An Idiot's Guide to Sudoku

If you don't know how to play sudoku, shame on you. But don't worry, it's incredibly easy to learn but ridiculously difficult to be fast.

What is Sudoku?!
Sudoku is a puzzle where you fill in some numbers. There are 81 squares (9x9) in the "playing field" with nine small squares and nine smaller boxes inside those. You must try to put in a number from 1-9 in each box. "Try?!" You say? TRY! You must follow these rules: each nine box square (a box with nine smaller squares and they don't overlap so there are exactly nine of them in the total area) can only contain the numbers 1-9 once. Each row and each column can only have the numbers 1-9 once. Get it? Basically, each number can not have the same number on that row or column, nor its little box of three by three.

Help!
The most basic strategy is knowing when a number cannot exist in that square. For example, if a row had the number 2 in it, then all other empty squares in that row cannot have the number 2, eliminating that from all possible choices. This same strategy should be applied to columns and individual boxes. Knowing where numbers shouldn't be is only half of it! Knowing where they should be is far more important as you'll be able to actually use that pencil. If a row, column or box has eight of the numbers filled, then the ninth should be easy to fill in. Getting to that point can be difficult; luckily, you can always cheat a little. If you have six numbers in a row, column or box, then you've eliminated the squares into three possible numbers. From those three squares, check all rows, columns and boxes linked to those and see if the numbers have already been in use; if they have, then you can eliminate more numbers from those three boxes. This may sound a little confusing at first but it'll make sense once you get started; just remember, you're using two strategies and combining them.

Helping you with this is the commonly used 'dot-strategy'. Basically, you draw dots on the paper so that you know which ones can or cannot be the number that you want. This is usually called "brute force" because you're checking for all possible combinations. This works just about every time unless the puzzle requires guessing. You'll know if this is the case if the puzzle can lead to multiple direction (more than one solution, but usually only one of the guesses will be correct). If this is true, you'll just have to guess and hope that it works; if it doesn't, go back or start over. I prefer starting over as that usually uses less time than trying to figure out how to go back.

Finish the Puzzle!
Unless you have only three or four blank squares remaining, you must finish the puzzle! Not only for the satisfaction in knowing that you can complete one but also that the most difficult part can be at the end. When there are about twenty of so blanks left, you'll feel bored but you should continue! Finish the Puzzle!

Of course, have fun while doing this because you'll be giving your brain a workout. Doing this just once a day could help you think, learn and memorize quicker than before. The advantageous of doing Sudoku far outweigh the disadvantageous (usually around 20 minutes) so you should always do them when you have the time!