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+/*
+ * Sudoku: A plugin for the Video Disk Recorder
+ *
+ * See the README file for copyright information and how to reach the author.
+ *
+ * $Id: solver.h 11 2005-10-28 01:00:01Z tom $
+ */
+
+#ifndef VDR_SUDOKU_SOLVER_H
+#define VDR_SUDOKU_SOLVER_H
+
+#include "sudoku.h"
+#include "backtrack.h"
+#include "puzzle.h"
+
+
+namespace Sudoku
+{
+
+  //--- class Sudoku::Solver ---------------------------------------------------
+
+  /** Implementation of a backtracking algorithm to solve Sudoku puzzles
+   *
+   * The algorithm tries to set numbers in all free cells of the puzzle
+   * sticking to the rules of Sudoku puzzles.
+   *
+   * There are three ways to use this class:
+   *
+   * 1. Solve a Sudoku puzzle with some numbers given:
+   *
+   *    \code
+   *    Puzzle puzzle(36); // Generate a random puzzle with 36 givens.
+   *    Solver solver(puzzle);
+   *    solver.find_next_solution();
+   *    if (solver.solution_is_valid())
+   *    {
+   *      // Do something with the puzzle.
+   *      ...
+   *    }
+   *    solver.find_next_solution();
+   *    bool more_than_one_solution = solver.solution_is_valid();
+   *    \endcode
+   *
+   * 2. Search a random Sudoku solution:
+   *
+   *    \code
+   *    Puzzle puzzle; // Generate an empty puzzle without givens.
+   *    Solver solver(puzzle, true);
+   *    solver.find_next_solution();
+   *    if (solver.solution_is_valid())
+   *    {
+   *      // Do something with the puzzle.
+   *      ...
+   *    }
+   *    \endcode
+   *
+   * 3. Search all Sudoku solutions:
+   *
+   *    \code
+   *    Puzzle puzzle; // Generate an empty puzzle without givens.
+   *    Solver solver(puzzle);
+   *    solver.find_next_solution(true);
+   *    while (solver.solution_is_valid())
+   *    {
+   *      // Do something with the puzzle.
+   *      ...
+   *      solver.find_next_solution(true);
+   *    }
+   *    \endcode
+   */
+  class Solver : public BackTrack::Algorithm, public BackTrack::Solution
+  {
+    Puzzle& puzzle;
+    Pos free_list[SDIM];
+    unsigned int free_count;
+    bool random_init, random;
+
+  public:
+
+    /** Constructor */
+    Solver(Puzzle& puzzle, bool random_init = false, unsigned int max_iter = 0);
+
+    /** Set the element to the first sibling. */
+    virtual void set_first_at(unsigned int level);
+
+    /** Set the element to the next sibling. */
+    virtual void set_next_at(unsigned int level);
+
+    /** Reset the element. */
+    virtual void reset_at(unsigned int level);
+
+    /** Check if the element is set to the last sibling. */
+    virtual bool is_last_at(unsigned int level) const;
+
+    /** Check if the element is valid (following elements ignored). */
+    virtual bool is_valid_at(int level) const;
+
+    /** Check if the level is the last possible level. */
+    virtual bool is_last_level(int level) const;
+  };
+
+} // namespace Sudoku
+
+#endif // VDR_SUDOKU_SOLVER_H