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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: generator.h 11 2005-10-28 01:00:01Z tom $
+ */
+
+#ifndef VDR_SUDOKU_GENERATOR_H
+#define VDR_SUDOKU_GENERATOR_H
+
+#include "sudoku.h"
+#include "backtrack.h"
+#include "puzzle.h"
+
+
+namespace Sudoku
+{
+
+  //--- class Sudoku::Generator ------------------------------------------------
+
+  /** Implementation of a backtracking algorithm to generate Sudoku puzzles
+   *
+   * To generate Sudoku puzzles two nested backtracking algorithms are used.
+   * First a random Sudoku solution is searched. Then the algorithm tries to
+   * remove some numbers so that only the requested number of givens remains.
+   * Each puzzle is checked with the nested solver algorithm if there is only
+   * one solution.
+   *
+   * Example:
+   *
+   * \code
+   * Puzzle puzzle;
+   * Generator generator(puzzle, 36);
+   * generator.find_next_solution();
+   * bool found = generator.solution_is_valid();
+   * \endcode
+   */
+  class Generator : public BackTrack::Algorithm, public BackTrack::Solution
+  {
+    Puzzle& puzzle;
+    Puzzle sudoku;
+    unsigned int free_list[SDIM];
+    unsigned int free_count;
+    Pos pos_list[SDIM];
+    unsigned int pos_count;
+    bool symmetric;
+    bool free_center;
+
+  public:
+
+    /** Constructor */
+    Generator(Puzzle& puzzle, unsigned int givens_count,
+              bool symmetric = true, 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_GENERATOR_H