🔢 Sudoku and Logic Games

The puzzle appeared in an American magazine in 1979 under the name Number Place. Its inventor was Howard Garns, a retired architect from Indianapolis, and he was not credited at the time — his name shows up only as a recurring entry in the contributor list of the issues that carried his puzzles. Nikoli, a Japanese puzzle publisher, picked it up in 1984 and gave it a Japanese name, later shortened to the four syllables everybody now uses. In 2004 it came back to the English-speaking world through a retired Hong Kong judge who had written a program to generate the grids, and within a year it was in every newspaper on earth.

Garns died in 1989. He never saw any of it.

Seventeen

There is one number that says more about the nature of this puzzle than any review could.

The minimum number of given digits for a grid to have exactly one solution is seventeen. That is not an editorial convention or a rule of thumb — it is a proved result. In 2012, Gary McGuire, Bastian Tugemann and Gilles Civario at University College Dublin exhaustively searched the space of possible sixteen-clue puzzles and demonstrated that not a single one of them has a unique solution. The computation consumed millions of processor hours.

Why it matters at the keyboard: if a grid shows fewer than seventeen filled cells, it either has more than one answer or the game is hiding some of them from you. And if there is more than one answer, you are not deducing — you are guessing, and the frustration you felt was correct.

"Hard" does not mean "empty"

The most common misconception in the genre, and cheap generators exploit it.

Removing digits makes a grid emptier. It does not necessarily make it harder. Difficulty is which technique you need to make the next move. If you can look at a row and see that only one number is missing, that is easy regardless of the clue count. If instead you have to notice that two cells in a box can only hold two particular digits — and that those two digits therefore vanish from every other cell in the box — that is harder. That pattern is called a naked pair, and it is the first rung above the beginner level.

Proper generators measure it by running a solving program, recording the most advanced technique it needed, and grading from that. A thirty-clue grid can be harder than a twenty-four-clue one, and any game that grades difficulty by counting blanks is guessing.

What is here

Fourteen real sudoku games sit in this catalogue, and they are not interchangeable: one offers 4×4 and 6×6 boards alongside the full 9×9, one pairs sudoku with futoshiki — the variant with greater-than signs between cells — and one abandons the classic grid entirely.

Beneath them the page fills from the wider logic shelf, four hundred and nine games: nonograms, fitting puzzles, deduction, path-finding. They are close relatives, in that they ask the same thing of you — see the constraint before you move.

What is missing is killer sudoku, and crosswords, which need hand-written clues and are therefore journalism rather than game development. Neither is here, and it is better said now than found out later.