Sudoku board
How it works
Constraint propagation + search
The solver reduces each cell’s domain before branching. Search is used only when propagation cannot determine the next value.
Domains
Every empty cell tracks digits not already used in its row, column, or 3×3 box.
Propagation
Naked and hidden singles reduce domains until no more forced assignments remain.
MRV backtracking
The solver branches on the cell with the fewest candidates, tries a value, and reverses the choice if it reaches a contradiction.
Complexity and limits
Generalized Sudoku solving is NP-complete. Backtracking has exponential worst-case behavior, although propagation and MRV reduce practical search. A solved board demonstrates algorithm behavior, not puzzle difficulty calibration.