Gaps

Rules

Blacken some cells in the grid such that each row and each column contains exactly two blackened cells. The numbers to the left of (or above) the grid indicate the number of unblackened cells between the cells in that row (or column). Blackened cells may not touch each other, not even diagonally.

(Rules and example from PGP IB)

History of the puzzle

Invented by Erich Friedman (USA) in 2010. His first set of puzzles can be seen in his website. It may have been independently invented elsewhere considering its simple rules.

Variants

Coral + Star Battle

See Coral#Coral + Star Battle.

Gaps between Battleships

See Battleships#Gaps between Battleships.

Appearances in the past WPCs

• WPC 2019/World Cup Round 2 by Jürgen Blume-Nienhaus
• WPC 2019/Team Playoffs (Coral + Star Battle) by Christian Halberstadt
• WPC 2018/Round 2 by Jiří Hrdina
• WPC 2018/Round 6 (Gaps between Battleships) by Jiří Hrdina
• WPC 2017/Round 16 by Rajesh Kumar
• WPC 2016/Round 16 by Matúš Demiger