Kurodoko is also called Kuromasu. Both names are used for the same shading puzzle from Japan.
The rules
- Shade some of the empty squares dark. Squares with a number always stay light.
- Each number must see exactly that many light squares, counting its own square.
- A number looks straight up, down, left and right. Its view stops at a dark square or the edge of the board.
- A number also sees past other numbers, because number squares are light.
- Dark squares may meet at a corner, but never side by side.
- All light squares must stay joined together along their sides.
Quirk uses the classic rules of the puzzle.
A worked example
Example 1: a 5 and a 2
The board is 3 by 3. A 5 sits in the top left corner. A 2 sits on the right edge, in the middle row. All other squares are empty.
- The 5 can look right along row 1 and down column 1. That is 2 squares each way.
- With its own square, the 5 can see 5 squares at most. So it needs all of them. Keep row 1 and column 1 light.
- Now look at the 2. It counts itself, and it sees the light square above it. That makes 2 already.
- So the 2 must not see any more. Shade the square to its left, in the centre of the board.
- Also shade the square below the 2, in the bottom right corner.
- One empty square is left, in the bottom row, middle column. It sits next to both dark squares, so it cannot be dark. Keep it light.
- Check: the dark squares only meet at a corner, and all light squares are joined. The puzzle is solved.
Example 2: two 4s
The board is 3 by 3 again. There is a 4 in the top left corner and a 4 in the top right corner.
- Each 4 needs to see 3 squares besides itself.
- Look at the top middle square. If it were dark, each 4 could see at most the 2 squares below it. With itself, that makes 3, not 4.
- So keep the top middle square light. Now each 4 sees the whole top row: itself and 2 more.
- Each 4 needs just 1 more square, below it. Keep the square just below each 4 light.
- Then shade the bottom left and bottom right corners, so the 4s see no more.
- The bottom middle square sits next to both dark squares, so it stays light.
- The centre square stays light too. If it were dark, the bottom middle square would be cut off.
Beginner techniques
Count the most a number can see
Count all the squares a number could see if nothing were dark. Add 1 for its own square. If that equals the number, keep all those squares light.
Stop a number that sees enough
When a number already sees enough light squares, its view must end there. Shade the next open square in each direction.
Light around dark
Dark squares never touch side by side. So every square next to a dark square, side by side, is light.
Share the count
If a number sees little one way, it must see more in the other ways. A 7 in a corner can only look 2 ways.
If the row to its right has 3 squares, at least the first 3 squares below it must be light.
Keep a way out
All light squares must join up. A light square in a corner needs at least one light square next to it. If shading a square would cut off light squares, keep it light.
Common mistakes
- Forgetting to count the number's own square.
- Stopping the count at another number. Numbers do not block the view.
- Shading 2 squares side by side.
- Closing in a light square, often in a corner.
- Shading a square with a number in it. Numbers always stay light.
Questions
Is Kurodoko the same as Kuromasu?
Yes. They are two names for the same puzzle. The rules are the same.
Does a number see past another number?
Yes. Number squares are light, so the view goes on past them. Only a dark square or the edge stops it.
Do I have to mark the light squares?
No. In Quirk, open squares count as light without a mark. Marking a square as light can still help you remember.
Is Kurodoko like Heyawake or Hitori?
They share two rules: dark squares never touch side by side, and all light squares stay joined. In Kurodoko, the numbers tell you where to shade by counting what they see.
Does every puzzle have one answer?
Yes. Every Kurodoko board in Quirk has exactly one answer. You can find it by thinking, step by step.
What sizes are there?
The easiest boards are 4 by 4. Harder boards grow up to 8 by 8.
Related puzzles
Playing it in Quirk
Tap a square to shade it dark. Tap again to keep it light, and once more to clear it. Drag over squares to give them all the same mark as the first one.
Open squares count as light, so you only need to shade the dark ones. Hints, undo and reset are there if you get stuck.
