All Sudoku Variants
9×9 · Arithmetic

Japanese Sums Sudoku

Ordinary Sudoku where some cells are shaded out; an outside clue lists the sums of the unshaded blocks in that row or column, in order.

5 3 4 7 8 9 1 212 27

An example Japanese Sums puzzle: a shaded cell splits row 1 into blocks summing to 12 (5+3+4) and 27 (7+8+9+1+2).

Japanese Sums Sudoku is an ordinary Sudoku with some cells shaded out. Outside each row and column a clue lists, in order, the sums of the unshaded blocks — runs of white cells, each separated from the next by at least one shaded cell. You must work out both which cells are shaded and what the white ones hold.

The rule: sum the white blocks

The white cells still obey Sudoku — 1–9 in every row, column and region. Shading breaks a line into consecutive blocks, and the outside clue gives each block's total from the edge inward. A gap in the numbers marks where a shaded cell falls.

Solving strategy

  • Read the block count. Two numbers outside a line mean exactly one shaded cell splits it; three numbers mean two, and so on.
  • Use the totals as cages. Each block is a small sum of distinct digits — combination logic pins the possibilities.
  • Cross-reference shading. A cell shaded in its row is shaded in its column too, tightening both clues.

Common mistakes

  • Forgetting the shaded gaps. Blocks are always separated by at least one shaded cell.
  • Summing the whole line. Each clue number is one block, not the entire row or column.
  • Dropping ordinary Sudoku. The unshaded cells still form a valid 1–9 grid.

Can I play it here?

Not yet — Japanese Sums Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: