Sudoku Solver

It uses backtracking: it finds the first empty cell, tries each digit 1-9 that doesn't conflict with that cell's row, column, or 3×3 box, and recursively continues — if a later cell turns out to have no valid digit, it backtracks and tries the next possibility for the previous cell, until every cell is filled or every possibility is exhausted.

If no digit arrangement can satisfy every row/column/box constraint, the solver reports "No solution exists for this puzzle." If your starting grid has multiple valid solutions (which a properly-designed Sudoku puzzle shouldn't), the solver returns the first one it finds via its search order, not necessarily a uniquely "correct" one.

It relies on the backtracking search itself to fail (returning "no solution") if your starting digits already violate Sudoku's row/column/box rules — there's no separate up-front validation step, so a conflicting starting grid will correctly be reported as unsolvable rather than silently producing a wrong answer.

Yes — it's a well-known, uniquely-solvable 9×9 Sudoku puzzle commonly used to demonstrate solving algorithms, included so you can see the solver in action immediately without needing to transcribe your own puzzle first.