All Sudoku Variants
9×9 · Constraint

Hyper Sudoku

Also known as Windoku, NRC Sudoku

Adds four shaded 3×3 windows that must each also hold 1–9, on top of the normal boxes.

1 4 7 8

An example Hyper (Windoku) puzzle: each of the four shaded 3×3 windows must also hold 1–9.

Hyper Sudoku — often called Windoku or Windows Sudoku — takes an ordinary 9×9 grid and adds four extra 3×3 regions, drawn as shaded "windows" set in from the edges. Each window must contain the digits 1–9 exactly once, on top of the usual rows, columns and boxes. Those four extra regions pack the grid with so much constraint that Hyper puzzles are famously quicker and more elegant than they look.

The rule: four shaded windows

The four windows sit at fixed positions, each offset by one cell from a corner of the grid, so they never touch the outer border or each other. Fill the grid so that every row, every column, every 3×3 box and every shaded window holds 1–9 once. In the diagram the four coloured 3×3 blocks are the extra regions.

The four shaded windows are extra 3×3 regions, each needing 1–9 — set one cell in from the corners.

Why the windows are so powerful

Each window straddles the corners of four different boxes at once, so it ties parts of the grid together that plain Sudoku keeps separate. A digit placed in a box now also has to respect the window overlapping that box's corner, which chains deductions across the grid far faster than rows and columns alone. In practice, the four windows behave like four bonus boxes — and the cells where a window overlaps a box are the most constrained on the whole grid.

The "leftover" lines

Look at the cells the windows miss: the fourth and middle rows and columns (and the outer border) are not covered by any window. These leftover cells feel the extra constraint only indirectly, so they are usually the last to fall. A useful trick works the other way, too: since each window and its overlapping box share three cells, the digits a window still needs but the box already has must live in the three window cells outside that box — a small law-of-leftovers argument that cracks many Hyper grids.

Solving strategy

  • Treat windows as boxes. Scan them for hidden singles exactly as you would a 3×3 box.
  • Target the overlaps. A cell shared by a box and a window carries two region constraints — start where they meet.
  • Play windows against boxes. Compare what a window needs with what its overlapping box already holds to pin the outside cells.
  • Leave the leftover lines for last. The uncovered middle and edge cells resolve once the windows are filled.

Common mistakes

  • Forgetting a window is a full region. Each shaded 3×3 needs all of 1–9 — not just "no repeats with its box".
  • Misplacing the windows. They sit one cell in from the corners, not flush with them; the exact position matters.
  • Ignoring the overlaps. The shared cells between a window and a box are the richest clues — do not scan windows in isolation.
  • Dropping the ordinary rules. Rows, columns and boxes all still apply; the windows are an addition.

Can I play it here?

Not yet — Hyper 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: