Cross the Streams

Rules

Shade some cells so that all shaded cells are connected and no 2×2 square is completely shaded. The clues outside the grid describe the contents of the respective row or column. Each number corresponds to a contiguous group of shaded cells, the number indicates the length of that group. A question mark (?) corresponds to a contiguous group of shaded cells as well, but of unknown length. Two such groups are separated by one or more unshaded cells. An asterisk (*) corresponds to an unknown number of such groups, possibly none at all, of any lengths. For each row and column, the clues are given in correct order.

(Rule from WPC 2019 IB, example from the 19th 24hPC IB)

History of the puzzle

Invented by Grant Fikes (USA) in 2010. Descended from Paint by Numbers. First puzzle by Grant can be seen here.

Appearances in the past WPCs

• WPC 2019/Round 6 by Roland Voigt
• WPC 2017/Round 16 by Prasanna Seshadri