Solving Sudoku: Basic Strategies

Sudoku is a game of logic, and it is considered cheating to guess at where a number belongs.  Because it is based on logic, there are logic strategies that can be used to solve any sudoku puzzle.  Knowing these strategies can make solving sudoku a fun experience, rather than making you want to pull your hair out.

• Naked Pairs – Naked pairs are also called Conjugated pairs. The definition of naked pairs is a set of two candidate numbers in two cells that have the same unit in common.  In layman’s terms, this means a set of two numbers that could be in two squares that are in the same row, column or block.  If there are two empty squares and two numbers, how does this help you in solving?  Let’s assume the first two squares in your first column are empty. You need a 3 and a 5 in each of the first two rows.  Either number could go in either of those two empty squares.  That tells you that 3 and 5 are not in any other square in that 3x3 block. That also tells you that 3 and 5 will not be in any other squares in the first column, so you can eliminate them as options in the other squares. 
• Naked Triples – Naked triples are similar to naked pairs.  Instead of three numbers and three squares, however, naked triples have three squares and a total of three numbers in the same unit.  In other words, you do not have to have three candidate numbers in all three squares.  For example, if 4, 8 and 9 could be in two squares, and 8 and 9 could be in a third, you have a naked triple.  This allows you to remove 4, 8 and 9 as possibilities in every other square in that unit, whether the unit is a row, column or block.
• Naked Quads – These work the same as naked triples, but you have four squares and four numbers.  Remember that this is four squares in the same row, column or block.  Also remember that it is a total of four numbers, as in 3 and 7 in one square, 3 and 4 in one square, 3, 4, 7 and 9 in one square, and 4, 7 and 9 in the fourth square.
• Hidden Pairs – Hidden pairs work the same way as naked pairs, but they are not as obvious as naked pairs.  For example, you may have one square in a row where 3, 6, 4 and 9 are all candidates.  In a second square of that row, 1, 3, 6 and 8 are candidates.  In this case, 3 and 6 are the hidden pair.  This allows you to remove the other numbers from both squares.  Removing those candidates can help you fill in the squares with the pair, as well as other squares in the same row, column or block as those squares.
• Hidden Triples and Hidden Quads – Find the triples or quads in the same way that you find the hidden pairs.  From there, the triples and quads work the same way as the naked triples and quads.

While the basic strategies may not be enough on their own for advanced puzzles like the samurai, they will get you started on the way to solving sudoku puzzles with less frustration.