The rules of Kurodoko
Kurodoko — 黒どこ — or Kuromasu is a logic puzzle.
- Every cell ends up either white or black.
- A cell with a number in it is always white.
- A number is how many white cells it can see in a straight line — up, down, left and right — counting itself. A black cell or the edge of the grid stops the count.
- Two black cells never touch side by side. Corner to corner is fine.
- Every white cell must connect to every other white cell.
How to solve one
Count what a number sees
Start at the number and count outwards in all four directions, adding up the white cells. Then add one for the number’s own cell. Stop counting at a black cell or the edge of the grid.
Fill in around a black cell
The four cells touching a black cell are white.
When a number cannot reach any further
Count every cell the number could still reach. If that total equals the number, all of those cells are white.
When a number already sees enough
If the white cells a number can already see add up to its number, the next cell in each direction is black.
Split the number between directions
A number’s count is shared between its four directions. If three of them cannot supply enough, the fourth has to reach further, so the cells along it are white.
Keep the white cells connected
A cell that black cells have sealed off cannot be white. A cell that would split the white area in two cannot be black.