Sudoku Manual (Hand) Solutions

These solutions apply to the most common 9x9 with 3x3 regions format. Other grids may require adapted tactics. There are several strategies involving a combination of the following techniques. The first two techniques are performed at the outset and periodically throughout the solution process.

1) Cross-hatching, being the reading of rows (or columns) to identify firstly which three square line must have a certain number, and secondly, reading down the columns (or rows), discovering which of these squares must contain the number. Typically the number tested would be one which appears frequently in the initial puzzle.

2) Counting 1-9 in regions, rows, and columns. Counting based upon the last number discovered may speed up the search.

3) Marking candidate numbers in blank squares. There are two popular notations. One is to write in the possible numbers in subscript in the squares. The other is to use a pattern of dots with a dot in the top left hand corner representing a 1 and a dot in the bottom right hand corner representing a 9. Once a complete set of candidate numbers has been written out then a process of elimination soon arrives at an answer.

4) Peforming a what-if on squares with only two candidate numbers. Then repeat the steps as above until a duplication is found, in which case choose the alternative candidate number. This particular option requires a pencil and eraser. This approach may be frowned on by logical purists as too much trial and error but it can arrive at solutions fairly rapidly.