Now that you know how to generate standard Sudoku puzzles, it is time to learn how to make some special ones.
By “designer Sudokus,” I mean puzzles in which the clues form a particular pattern. For example, Figure 17-1 shows a “diamond Sudoku” (with difficulty level 3). I grayed the cells with the clues to highlight the pattern.
Figure 17-1. A diamond Sudoku
To implement designer puzzles, you need to modify sudoku_gen.c in such a way that instead of removing clues by pseudorandom choices, it removes ...