Little Killer Sudoku
Little Killer Sudoku is a cousin of Killer Sudoku with a twist of its own.
The base is familiar: every row, column and 3×3 block holds the digits 1–9
without repeats. On top of that, some diagonals are marked with arrows: the
digits along a diagonal sum to the number at its start on the grid edge.
The key difference from cages: digits along a diagonal may repeat! Rows and
columns still forbid duplicates, but a diagonal runs straight through — so
sums work differently here. A full nine-cell diagonal always totals exactly
45 — the rule of 45 in its purest form, a ready anchor point.
Every round is generated on the fly: the full solution comes first, arrows
are laid along the diagonals of that solution with honest sums, and open
digits are removed so that the solution stays unique.
The diagonals are drawn as lines with sums at the grid edge. Input is tuned
for phones: tap a cell, an on-screen digit pad, erase with a single button.
«Check» highlights mistakes, «Hint» places a correct digit. Three
difficulties: «Easy» — more open digits, «Hard» — up to eight arrows and a
nearly bare field.