Special Section: Sudoku The game of Sudoku exploded in popularity worldwide in 2005. Almost every major newspaper now publishes a Sudoku puzzle daily. Handheld game players let you play anytime, anywhere and create puzzles on demand at various levels of difficulty. Be sure to check out our Sudoku Resource Center at www.deitel.com/sudoku for downloads, tutorials, books, e-books and more that will help you master the game. And not for the faint of heart-try fiendishly difficult Sudokus with tricky twists, a circular Sudoku and a variant of the puzzle with five interlocking grids. Subscribe to our free newsletter, the Deitel Bazz Online, for notifications of updates to our Sudoku Resource Center and to other Deitel Resource Centers at www.deitel.com that provide games, puzzles and other interesting programming projects. A completed Sudoku puzzle is a 99 grid (i.e., a two-dimensional array) in which the digits 1 through 9 appear once and only once in each row, each column and each of nine 3x 3 grids. In the partially completed 9x9 grid of Fig. 6.27, row 1, column 1, and the 3x 3 grid in the upper-left cor ner of the board cach contain the digits1 through 9 once and only once. We use C's two-dimen sional array row and column-numbering conventions, but we're ignoring row 0 and column 0 in conformance with Sudoku community conventions. y blanks, often arranged in a The typical Sudoku puzzle provides many f symmetrical pattern as is typical with crossword puzzles. The player's task is to fill in the blanks to complete the puzzle. Some puzzles are easy to solve; some are quite difficult, requiring sophisti- cated solution strategies filled-in cells and man In Appendix D, Game Programming: Solving Sudoku, well discuss various simple solution strategies, and suggest what to do when these fail. Well also present various approaches for pro- gramming Sudoku puzzle creators and solvers in C. Unfortunately, Standard C does not include graphics and GUI (graphical user interface) capabilities, so our representation of the board won't be as elegant as we could make it in Java and other programming languages that support these capabil- ities. You may want to revisit your ming with the Allegro C Library. Allegro, which is not part of Standard C, offers capabilities that will help you add graphics and even Sudok u programs after you read Appendix E, Game Program- sounds to your Sudoku programs 151 3 4 9 7 6 28 Fig. 6.27 | Partially completed 9x9 Sudoku grid. Note the nine 3x3 grids.