In November 2006, I bought the book The Sudoku Code, by Francis Heaney and Frank Longo. This book contains 200 sudoku puzzles, half of which are actually "wordoku" puzzles, in which the nine symbols used are letters, rather than numbers. The solution to the numerical problem on each left-hand page selects nine letters from the solved wordoku on the right-hand page. These letters slowly build a clue to the final solution. The 200 puzzles are divided into five groups of 40, which get progressively harder as you go through the book. The levels are called "easy", "medium", "tricky", "hard", and finally, "cruel".
Although I've done so many sudoku puzzles that I'm pretty much tired of them, this book was strangely addictive. As the clue to the final solution gradually unrolled, I found myself very curious about what was going to come next. There are various twists and turns as the clue is revealed, which I leave you to discover on your own.
Since there are a total of 200 puzzles, arriving at the answer is quite a bit of work. I did use my spreadsheet to help me solve the puzzles, which some people might think is cheating. As far as I'm concerned, my spreadsheet simply automates the tedious discovery of constraints, which I could certainly do manually (and I did do many of the puzzles manually on the easier difficulty levels). To help me do the wordoku puzzles, I altered a version of my spreadsheet to allow me to enter the puzzle using the given letters. The spreadsheet then converts this into a numerical equivalent sudoku, which I solved in the usual way. Finally, the spreadsheet converts that solution back into the wordoku letter solution, using the same number-letter correspondence.
It might seem that I could have simply altered my spreadsheet to work directly in the letters for the wordokus. However, in my original spreadsheet, given that it was working with numbers, I made use of various numerical tricks in the spreadsheet formulas. Therefore, it was easier for me to convert each wordoku into a numerical puzzle, solve that as usual, and convert back, with the spreadsheet doing all the work.
If you're interested in playing with that spreadsheet, you can get it here. To download it in Windows, right-click on the link just below, and select "Save target as":
Although I certainly won't give any clues to the solution here, I will give you one tip that might help you work a bit faster. Since English has a great deal of redundancy, as the clue unrolls, it is often possible to guess at what is coming next, or at least a portion of it. To take advantage of this, I solved all of the wordokus first, and then went back to solve the numerical sudokus. As I did so, I was able to use guesses as to what was coming next from the corresponding wordoku to provide additional "givens" to help solve the numerical sudoku. This often made the solution to the numerical sudoku significantly easier, especially towards the end of the book, when the puzzles were in the "hard" and "cruel" categories.
There's a page at the end of the book on which you can write your final solution, and mail it in to the publisher. I got back a letter of congratulations from author Francis Heaney, and a button to wear that says, "I CRACKED THE SUDOKU CODE". You have to send in the actual page from the back of the book, and not a copy. Obviously, this is to ensure that they only send buttons to people who have actually bought the book.
One might argue that solving the puzzle is really too much work to do just for a button. But as I said, I had a lot of fun solving the puzzle. There's a lot of clever wordplay in both the "givens" and the solutions of the wordokus, and it kept me amused throughout.