Proposed by Gary Duncan, Ian Gent
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).