Sudoku Tips: Scanning by Counting

The most simple scanning technique is counting - select a row, column or region, and count the numbers in the cells in from 1 to 9, to identify the missing numbers.

Of course, this is most helpful when there is only one number missing from the row, column or region that you’re counting - then you know that number belongs in the missing blank cell.

Another counting technique is to select a blank cell, and work through the numbers 1 to 9, scanning the rows, columns and regions to determine which number uniquely belongs in that cell.

But what if your counting shows that two numbers are missing? Then you may be able to determine the correct number by eliminating one of the candidates by cross-hatching

In the Sudoku to the right, there are two blank cells in the third row. Counting reveals that the missing numbers are 2 and 6. But which number goes in which cell? Cross hatching shows that the 2 can only go in one of the two blank cells, which means that the 6 must belong in the other blank cell.

Most of the very simple Sudoku can be solved by a combination of counting and cross-hatching.