Games::Sudoku::PatternSolver - solve and generate standard 9x9 Sudoku.

 A lesser-known approach to solving sudoku by use of distribution patterns. (POM / Pattern Overlay Method)
 It is a recursive, nondeterministic, depth-first, backtracking way to tackle the 'Exact Cover Problem',
 just like Donald Knuth described 'Algorithm X', but very different from the DLX implementation.
 
 http://forum.enjoysudoku.com/new-solving-technique-i-think-t30444.html
 In any standard 9x9 sudoku's solution, the positions of every single number end up in one of 46656 possible patterns.
 The rules of the game, the number placing constraints, are inherently present in these patterns.
 They have been pre-created and come as a binary file included with this distribution. 
 
 By default, before the backtracking starts on a puzzle to solve, it is tried to fill more cells with some basic sudoku methods.
 (Naked/hidden singles, locked sets and locked candidates)
 This allows to roughly rate the puzzle's difficulty and speeds up the subsequent backtracking:   
     
 Solving the puzzle by patterns encompasses two phases:
  1. depending on count and positions, every symbol is assigned a reduced set of pattern candidates, according to its givens (typically between 4 - 900)
  2. in a backtracking process, candidates from all sets are tried to combine - inevitably leading to every solution possible

 Steffen Heinrich, Jan. 2024