Nonograms are a popular puzzle, which goes by different names in different
countries. Solvers have to shade in squares in a grid so that blocks
of consecutive shaded squares satisfy constraints given for each row and
column. Constraints typically indicate the sequence of shaded blocks
(e.g. 3,1,2 means that there is a block of 3, then a gap of unspecified
size, a block of length 1, another gap, and then a block of length 2).