Links to
Sudoku; or algorithms
1,
2,
3, or
4, or
5,
userguide
or download
If there is only a single remaining pencil mark
in a box for a given number (there may be other pencil mark in its
cell), then it must be a certainty, and all other pencil marks in
that cell can be rubbed out. All other pencil marks in the same box,
row, or column can also be rubbed out.
In the above example the numbers in red are
single candidates in a box. The blue numbers can then be rubbed out.
UPDATE answers
SET pencil_mark_ind = 0
WHERE pencil_mark_ind > 0
AND puzzle_id = p_puzzle_id
AND (box_id, answer) IN
( SELECT a.box_id,
a.answer
FROM answers a
WHERE a.puzzle_id =
p_puzzle_id
AND
a.pencil_mark_ind > 0
GROUP BY a.box_id,
a.answer
HAVING COUNT(*) = 1);
Like with the Singles Cell algorithm, if any
certainties have been identified, then any candidates that can be
eliminated need to be rubbed out using the same two steps described
before.
Just by iterating through the Singles  Cell
and Singles  Box steps over and over again, it possible to solve a
good proportion of the puzzle (see below). Anything less than a "The
Times Fiendish" will usually be completely solved with these two
algorithms.
The above shows how far the above puzzle can
get just on these two algorithms.
To view the other algorithms select the
required link...
1. Singles  Cell
2. Singles Box
3. Cross Hatching
4. Partial Members Set
5. Full Member Set
