PuzzleTeam defines the rules as:
The rules of sudoku are simple:
How I actually solve one — the reasoning I run before any code does, written out in full. Read down the right column; the board on the left follows whichever step you are on.
A Sudoku board is a grid carved into nine boxes, and every cell must end up holding a digit from 1 to 9. Before placing anything I size up the space, because the count of completed grids satisfying all three rules is known exactly:
Nothing enumerates a space like that, so I never treat the board as 81 independent choices. I treat it as 27 interlocking units — nine rows, nine columns, nine boxes — each of which must become a permutation of 1–9. Concretely, I keep one 9-bit mask per row, column, and box recording which digits that unit still needs, and every empty cell's candidate set is just the intersection of the three masks that cross it:
That frame is the whole engine. Placing a digit clears one bit from three masks, which shrinks the candidate sets of up to twenty peers at once — and on a daily puzzle, that shrinking is what solves the board, not search.
The robotic solver on real boards: the daily puzzle comes straight from the API, and the samples — Basic up to Evil — replay recorded solver runs move by move.