Questions
Kurodoko — 黒どこ — or Kuromasu is a logic puzzle.
- What is Kurodoko?
- Kurodoko is a Japanese logic puzzle published by Nikoli. You shade some cells black so that every number counts exactly the white cells it can see in a straight line. It uses no arithmetic beyond counting, and every puzzle has one answer that can be reached by reasoning alone.
- Is Kurodoko the same as Kuromasu?
- Yes. The full Japanese name is 黒マスはどこだ — “where are the black squares?” — which shortens to 黒どこ (Kurodoko) or 黒マス (Kuromasu). English-language puzzle books use both names for the identical puzzle, and older collections sometimes render the Japanese literally as “Where is Black Cells”.
- How do you solve a Kurodoko puzzle?
- Start with the numbers that can see the least. If a number already sees as many cells as it needs, everything still in its sight is white. If it cannot possibly see enough, the cells nearest to it must be white. Once a black cell is placed, its four neighbours are white, because black cells never touch.
- Can a numbered cell be black?
- No. A cell with a number in it is always white.
- Can two black cells touch?
- Not side by side. Two black cells may meet at a corner, but never share an edge.
- Do all the white cells have to be connected?
- Yes. A cell that black cells have sealed off cannot be white, and a cell that would split the white area in two cannot be black.
- How many black cells are in a puzzle?
- It varies, and the count is not given to you. On these grids roughly a fifth of the cells end up black.
- Does every puzzle have exactly one solution?
- Yes. Every puzzle here is checked by an independent solver before it is banked, and any grid with two answers is thrown away. You never have to guess.
- What is the difference between Easy, Medium and Hard?
- The grid size and the reasoning needed. Easy is 5×5 and asks only the simplest deductions. Medium is 7×7 and needs you to share a number’s count across its four directions. Hard is 9×9 and will need at least one chain where you assume a cell’s colour and follow it to a contradiction.
- When does a new puzzle appear?
- At midnight where you are. All three sizes change at once, and every past puzzle stays playable in the archive.
- Is it free? Do I need an account?
- It is free and there is no account. Your progress is kept in your own browser, so it survives a closed tab but does not follow you to another device.