Sole Number Technique is not a commonly used technique in Direct Elimination Techniques. It is easily understood but difficult to use because it can hardly be identified. Therefore, the use of this technique is often limited.
Compared with Sole Position Technique, Sole Number Technique determines which number can be assigned to a designated cell, while Sole Position Technique determines which cell can be placed with a designated number. In addition, Sole Position Technique is commonly used since it can be identified easily.
Compared to Candidates Elimination Techniques, Sole Number Technique corresponds to Naked Single Technique. While the fact is that Naked Single Technique is the simplest technique in Candidates Elimination Techniques. Sole Number Technique, however, is advanced and seldom used in Direct Elimination Techniques.
Let's look at an example first:
Which number is supposed to be assigned to cell [G9]? To answer this question is not easy if you use all the techniques that are introduced before. However, if we look at the column, row and block where it lies, we can find the fact that all digits from 1 to 9 occur except 2. Among them, 7, 6, 9, 5, 3 and 8 occur in Row G. 5, 8, 7 and 1 lie in Column 9. And 3, 8, 4, 7, 5 and 1 are in Block at [G1]. Therefore, in order not to violate the sudoku rule, the number to be assigned to [G9] must be 2.
The condition to apply Sole Number Technique is that if 8 out of 9 digits occur in the column, row and block where a cell lies, then the number to be placed in this cell must be the one that has not occurred yet.
Very simple, isn't it? In practice, however, it is very hard to identify. For example,
Can you find the exact cell that you can apply Sole Number Technique?
Try this one as well:
The answers are [E6] = 9 and [I7] = 9 respectively.
Generally speaking, this technique is only used when all basic elimination techniques fail to work.
See Also:
