killer sudoku: no starting digits, just cage sums. every dashed region's digits are unique and add up to the number in its corner — combine that with normal sudoku rules and the board cracks open.
a full solved grid is built with randomized backtracking, then chopped into 1–4 cell cages whose digits never repeat. a constraint-propagation solver (row/col/box rules + per-cage sum combinations, most-constrained- cell first) checks the cage layout has exactly one solution — if not, it reveals the fewest starting digits needed to force uniqueness, same trick real killer sudoku setters use. today's puzzle is seeded from the UTC date, so it's the same for everyone.