pseudocoup - (3*3)x(3*3) sudoku solver

  pseudocoup [ options ] [ puzzle ... | < puzzle.file ... ]

  pseudocoup solves (3*3)x(3*3) sudoku puzzles defined by the literal puzzle
  operands or puzzles read from the standard input if there are no puzzle
  operands, and solves each puzzle. A solvable puzzle has exactly one solution.
  The solver stops on the first solution for each puzzle.

  There are a few compile time options that may degrade performance.  Other
  compile time options control puzzle order (4..64) and QWH (quasigroup
  with holes or latin square) vs. sudoku.  See the source for details.

  pseudocoup is coded for solving speed.  It uses only two simple constraints:
    F  Forced cell: only one value possible.
    N  Only cell: only one value in row/col/box.
  When the constraints fail to make progress a guess is made and the solver
  backtracks.  Guesses are made on solution cells that minimize the maximum
  number of holes for all candidate values for the cell using a 1 level
  forward check.  Ties go to the cell with the least number of candidate
  value constraints.

  Puzzle input is a sequence of (3*3)x(3*3) characters that fill the grid from left
  to right, top to bottom.  Space separated numbers are clue values,
  #...newline, //...newline, "...", [...], and <...> are comments, {...}
  or digit strings separated by space are candidate values (hints), and
  all other characters not matching [[:space:]|*+-] are treated as an
  empty grid space.  Invalid puzzles produce a diagnostic.  Each puzzle
  description may be followed by 0 or more [R,C]=V or [R,C]={ABC} operations
  that set the cell value at row R column C to V or the candidate values to.
  'ABC' .

  A comment line containing the puzzle ordinal, and puzzle line if different
  from the ordinal, is printed for each puzzle, followed by the solution
  in grid form.

  Solution speed on a collection of posted and generated puzzles is
  ~7000 puzzles/second/Ghz.  Minimal puzzle generation speed is
  ~10 puzzles/second/Ghz.

  sudoku(1), sudocoo(1)

  version     pseudocoup (3*3)x(3*3) (AT&T Research) 2007-10-11
  author      Glenn Fowler 
  copyright   Copyright (c) 2005-2007 AT&T Knowledge Ventures