Sudoku books

A sudoku book is a layout book whose pages are generated from nothing. You name the pages and choose a difficulty; the app makes every grid, guarantees each one has a single solution, and builds the answer key.

It is the only book here you can fill without writing anything. A word search still needs your word lists — a sudoku needs only the pages themselves.

There is no AI art step. A sudoku is arithmetic, not illustration, and charging image credits for one would be absurd. The only thing you can spend credits on is an optional page border, which works exactly as it does for a word search.

Making the book

1. Set the page count on the page plan, the way every layout book does.
2. Choose a grid size. One size for the whole book — pages at different sizes read as a mistake.
3. Name the pages. Either type the names yourself or use ✦ Page plan, which proposes titles and paces them so the book gets harder as it goes. There are no word lists to write.
4. Choose a difficulty in the Puzzles step.
5. Press Generate. The whole book is made locally, for nothing. A 9x9 book of sixty pages takes a couple of seconds; a 16x16 takes a couple of minutes, and shows a running count while it works.

Grid sizes

Above 9x9 a cell prints a letter once the digits run out: 1-9 then A-C for a 12x12, 1-9 then A-G for a 16x16. That is what the published Dodeka and Hexadoku books do, and it is what keeps every cell a single character so the grid stays crisp at any size. (Some 16x16 books use hexadecimal 0-F instead; this one does not, because that scheme starts at zero and does not carry over to 12x12.)

A 4x4 or 6x6 is always easy, and the difficulty control says so rather than offering a setting it cannot honour. There is not enough grid for a deduction that needs anything beyond singles.

Difficulty is measured, not set

This is the part worth understanding, because it is where the app will sometimes tell you something you did not ask to hear.

The obvious way to grade a sudoku is to count how many digits are printed — "easy is 36 givens, hard is 24". That is wrong in a way that gets a book returned: how much of the grid is blank says very little about how hard the deductions are, and two puzzles with identical given counts can be a minute apart to solve.

So a puzzle is graded by which techniques it actually requires:

Because the grids are carved by a seeded process, the occasional page cannot reach the difficulty you asked for while still having exactly one solution. When that happens the page is printed at the difficulty it really is, and the Puzzles step names the pages it affected. A book that quietly labelled those pages "hard" would be lying to the reader on the cover.

In practice this is rare — the generator tries several ways of carving each grid and keeps one that hits the target — but it is never zero, so the Puzzles step tells you rather than leaving you to find out from a review.

Every puzzle has exactly one solution

This is checked as each grid is made: a digit is only removed if the puzzle still resolves to a single answer. It is the one fault a reader is guaranteed to notice — they fill the grid in good faith, disagree with the key at the back, and conclude the book is broken.

The grids are stable

Each puzzle is derived from its own page, so regenerating redraws the book exactly as it was. A page you have already proofed will not quietly become a different puzzle because you pressed the button again.

The cost of that is there is no re-roll: if you dislike a particular grid, there is currently no way to ask for another one on that page.

The answer key

Turned on by default. The key is added as pages at the back of the book, twelve solutions to a page by default, and each solution is numbered with the same number its puzzle prints in its own footer — so a solver looking up "Puzzle 7" finds puzzle 7.

Unlike a word search, there is only one way to print a sudoku solution: the filled grid. A word search offers a highlighted key and a dotted one because a solver has to be shown where the answer is. A sudoku's answer is the whole grid.

The key adds pages, and page count moves the spine, the print cost and the release checks. The Puzzles step says how many it added or removed each time.

Page layouts

Three, in the gallery:

All three draw the grid the same way: a hairline rule at every cell and a heavier one at every region boundary — every three cells on a 9×9, every four across and three down on a 12×12. Both weights are adjustable per layout, along with how much of the page the grid takes.