All Sudoku Variants
9×9 · Constraint

Extra Regions Sudoku

Also known as Extra Region Sudoku

Additional nine-cell regions, of any shape, must also contain the digits 1–9 without repeating — on top of the usual rows, columns and boxes.

1 4 6 8 9 5 7

An example Extra Regions puzzle: the shaded staircase is a bonus nine-cell region that must also hold 1–9.

Extra Regions Sudoku adds one or more bonus nine-cell regions to the grid, each of which must also contain the digits 1–9 exactly once. Unlike the neat 3×3 windows of Hyper Sudoku, these regions can be any connected shape — a staircase, an L, a zig-zag — which is exactly what makes them interesting to solve.

The rule: a bonus region needs 1–9 too

Wherever an extra region is shaded, treat it as a tenth "box": all nine of its cells must hold the digits 1–9 with no repeats, on top of the usual rows, columns and boxes. The shaded staircase below is one such region — nine connected cells winding diagonally across the grid, each of which must be a different digit.

The shaded staircase is one extra region — nine connected cells that must hold 1–9, like a box of any shape.

How it differs from Hyper Sudoku

Both variants bolt extra nine-cell regions onto the grid, but Hyper Sudoku always uses the same four 3×3 windows in fixed positions. Extra Regions puzzles are free-form: the setter can draw a region that snakes across several boxes, cutting through rows and columns at odd angles. That freedom lets a region overlap the standard boxes in unusual ways, which is where its solving power comes from — a shaded region sharing, say, two cells with one box and two with another ties those boxes together.

Using the extra region

The trick is the law of leftovers. Compare the extra region with the rows, columns or boxes it overlaps: the cells the region includes but a box does not must hold the same set of digits as the cells the box includes but the region does not. A snaking region that borrows a few cells from each of several boxes hands you those leftover relationships all over the grid, and they resolve cells no ordinary scan can reach.

Solving strategy

  • Treat the region as a box. Scan it for hidden singles exactly as you would a 3×3 box.
  • Map the overlaps. Note which standard boxes, rows and columns the region shares cells with — those are your leftover pairs.
  • Work the law of leftovers. Match the region's cells against an overlapping unit to pin the digits that must live in the difference.
  • Feed the grid. Every digit the region forces behaves like a given for its row, column and box.

Common mistakes

  • Forgetting a region is a full unit. All nine cells need 1–9 — not merely "no repeats with the boxes they touch".
  • Assuming a fixed shape. Unlike Hyper's windows, an extra region can be any connected shape; read the grid, don't assume.
  • Missing the overlaps. The region's real value is where it shares cells with standard units — scan those, not the region alone.
  • Dropping the ordinary rules. Rows, columns and boxes all still apply on top of the extra region.

Can I play it here?

Not yet — Extra Regions 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: