A zerodoku consists of a grid containing N x N cells.
Each cell contains a number ranging from zero to 9.
The groups consist of the rows and columns. Boxes are not involved.
Within a group, zero can occur at most twice.
The cells containing zero are breaking the groups into pieces called segments. The cells containing zero are not part of the segments.
Within each segment:
– No digit can occur more than once
– The digits form a series – possibly permuted.
For example, if a segment would consist of 3 cells, it could contain 2|1|3 or 6|8|7, but 2|5|4 would be invalid.