Sudoku is an exact cover problem — 729 candidate placements against 324 constraints — and
Knuth's dancing links solves any grid essentially instantly. The generator leans on that: it
strips cells one at a time, re-solving after each to guarantee the puzzle still has exactly
one answer.
Arrow keys to move · 1–9 to enter · 0 or Backspace to clear · H hintTap a cell, then tap a number