Puzzle guide

How to solve Kurodoko

In Kurodoko every number is a lookout. It counts the white cells it can see along its row and column, its own cell included, until a black cell or the edge blocks the view. You make cells black until every number sees exactly its count.

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The rules

Make some cells black. A cell with a number is never black.
A number counts the white cells it sees up, down, left and right, its own cell too. A black cell or the edge blocks the view.
Black cells never touch side by side. Corner to corner is fine.
All the white cells stay joined together.

A solved puzzle

A solved puzzle. The 9 at the bottom sees itself, four cells up and two to each side. Black cells never touch side by side, and all white cells are joined.

Your first moves

Start with big numbers: they need to see far, so the cells close to them are white.
Start with small numbers too: a 2 sees just one other cell, so its view must be blocked very soon.
Around every black cell, the four neighbours are white. Mark them with a dot.
Keep the white area in one piece: a black cell must never cut it in two.

Techniques, step by step

Around a black cell

Black cells never touch side by side. So as soon as a cell is black, its four neighbours are white. Mark them with a dot. Each dot makes the view of the numbers nearby a little longer.

The four neighbours of a black cell are white.

A number that already sees enough

The 2 in the corner counts itself and the white cell beside it: that is already 2. It must not see any more, so the next cell along each direction is black: the cell after the white one to the right, and the cell right below. Whenever a number already sees its count with the cells you know are white, block every view right there.

The 2 sees two cells, so both views end here.

A number that needs everything

This 5 stands in the middle of a small puzzle. Even if every cell around it is white, it sees itself and four more: exactly 5. So it needs all of them. Every cell it can reach is white. Big numbers near the edge often work the same way.

The 5 needs every cell it can see, so they are all white.

Share the count between directions

A number's count is split over four directions. If three directions together can show at most a few cells, the fourth must show the rest, and that often reaches far enough to make several cells white at once. Turn it round too: if one direction already shows a lot, the others may only show a little, so a black cell has to come soon.

Keep the white cells joined

All white cells must stay connected. The white corner cell has a black cell to its right, so its only way to the rest is down. If that cell were black too, the corner would be shut in. So it stays white. Check this near corners and edges every time you make a cell black.

The corner has one way out, so that cell stays white.

Common mistakes

Forgetting the number's own cell. A number counts itself. A 1 means it sees nothing else: all four neighbours are black or the edge.
Counting past a black cell. The view stops at the first black cell in each direction.
Black cells side by side. Corners may touch, sides may not.
Cutting off white cells. The app does not mark white cells cut off from the rest, so check the white area yourself.

Questions and answers

What is Kurodoko?

A Japanese logic puzzle where you blacken cells so that each number sees exactly that many white cells along its row and column, counting itself. It is also called Kuromasu.

Does a number count its own cell?

Yes. A number always sees at least itself, so a 1 sees no other cell at all.

How do I make a cell black or white?

Tap a cell to make it black, and tap again to clear it. Press and hold to mark it white with a dot. Drag to make several cells black at once.

Is Kurodoko the same as Kurotto?

No. Kurotto counts the sizes of the shaded groups touching a circle. Kurodoko counts the white cells a number can see in straight lines.

Where should I start?

With very small and very large numbers, then with dots around every black cell. After that, share each number's count between its four directions.

Ready to play?

Block the views of numbers that already see enough, open them for numbers that need everything, and keep the white cells joined. That is how a Kurodoko comes into view.