Archive for June, 2009

Sudoku Solving Techniques

When you first look at a Sudoku puzzle, you should take some time to analyze the grid. The video tutorials advertised to the right demonstrate the sudoku solving techniques you need. I will briefly cover the most important in the following.

Scanning

The initial analysis is often referred to as scanning. You should scan the puzzle at least once initially and again as you successfully identifies and places numbers in the empty cells.

The first thing you want to check for to solve any sudoku puzzle is where the most given numbers are. You are more likely to identify the correct number to place in a cell if there are less options. You should start with the region, row or coloumn with most numbers already given.

Next you want to look for frequency of numbers. Again, you are more likely to find a solution where there are fewer options. You should start with the number with the highest frequency, then the next higher frequency – and so on.

To make a start, look at the region with most given numbers and ask yourself questions like “if I put a 1 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?”

No matter what level of puzzle you are attempting to solve, you will soon discover keeping track on which numbers are possible solutions in which cells, is quite challenging – Especially if this your first attempt to solve sudoku puzzles.

Subscript Marking

You should use subscript marking to note possible numbers in the cells. Solving a Sudoku puzzle require a structured approach, and keeping track of your possible numbers is necessary. As you develop your skills and master the sudoku solving techniques, you will be able to solve easy puzzles without this technique.

The one disadvantage to this is that many puzzles, such as those found in newspapers, the grids are often too small to allow you to write more than one number in each cell. Consider making a larger copy of the puzzle so that you can read it easier or use a pencil that is very sharp so that you can write with a fine hand.

A puzzle will be classified as “easy” if you can solve it by the scanning method alone. Sudoku puzzles that are more challenging won’t be solved by scanning alone but will need multiple solving techniques.

Sudoku Solving Strategies

No matter what level of puzzle you are attempting to solve there are two basic strategies that will allow you to find and place correct numbers in empty cells. These sudoku solving strategies are demonstrated in sudoku video tutorials advertised to the right.

Counting

Counting is the process of counting from 1 to 9 in row, columns, and regions so that you can tell if there are any missing numbers. The main rule of sudoku: “if a number is right for a cell, this is true for the region and the intersecting row and coloumn is important here. You don’t count the region, row and coloumn separately. You should start with one cell and then check the presence of numbers 1 through nine for the region and the intersecting row and coloumn.

If you are working harder puzzles the value of one single cell can often be determined by counting in reverse. This is done by scanning the region, the row, and the column for numbers that can’t be right to see which numbers are left that might work.

Cross-hatching

Cross-hatching starts by scanning the rows and columns to see if the presence of a number in the row or coloumn blocks any cells in the region. The main rule of sudoku – if a number is right for one cell, this is true for the region, row and coloumn – also applies here. A number given in a cell in a row or a coloumn, will not occur in any region intersected by this row or coloumn.

You repeat the process for every row and column. To make things even faster, scan the numbers in their order of frequency. Perform cross-hatching systematically by checking for all the digits from 1 to 9 in order.

Guessing

Try not to guess. Until you have progressed to the tough and diabolical puzzles, guessing is not only totally unnecessary, but will lead you up paths that can make the puzzle virtually unsolvable. Simple logic and a structured approach is all that is required for gentle and moderate puzzles. Most puzzles that are rated easy to hard will be solved by the basic strategies and a minimum of analysis.

Contingencies

Once you become advanced in solving Sukoku Puzzles you will learn to look for what are called contingencies while you are scanning. This means that you will narrow down the location of a number within a row, column, or region to two or three cells. When each of those cells fall into the same row, or column, of the region, then you can use them to eliminate other numbers by cross-hatching and counting.

Sudoku puzzles that are really challenging might require you to try multiple contingencies. There will be times when you have to recognize these contingencies in multiple directions while at times even intersecting your number selection.

A sudoku puzzle will be classified as “easy” if you can solve it by the counting and cross-hatching alone. More challenging sudoku puzzles will need more advanced sudoku solving strategies.