This version adds the following features: naked
quadruplets reduction, hidden quadruplets
reduction, swordfish reduction, the -e option to
put in explanatory mode, the -i option to ignore
some solving techniques, the -l option to rate the
level of difficulty, support for pipes (by reading
from standard input), and improved readability of
messages.
New solving techniques are supported: naked triplets reduction and hidden triplets reduction. There is a -u option to test the unicity of the solution, and an -m option to modify the string.
This version added a -s option that provides suggestions about the next step, a -p option that probes the Sudoku using a particular technique, a -o option that obtains only the first solution in the case of a multiple solutions puzzle, and a -n option that disables backtracking. More solving techniques are supported, including block to row/col reduction, block to block reduction, naked pairs reduction, hidden pairs reduction, and x-wing reduction.
