Lighthouses

Rules

Locate ships in the grid such that each “lighthouse” (clue with a given number) indicates the number of ships in the same row or column as that lighthouse (it “sees through” other lighthouses and other ships). Each ship occupies a single cell and does not touch other ships or lighthouses, not even diagonally.

(Rules and example from PGP IB)

History of the puzzle

Probably first appeared on WPC 1993. The author of the puzzle is unknown.

Appearances in the past WPCs

• WPC 2019/Round 11 (Triangular) by Erhard Notz
• WPC 2018/Round 2 by Jiří Hrdina
• WPC 2017/Round 7 by Prasanna Seshadri
• WPC 2013/Part 9
• WPC 2012/Part 5
• WPC 2011/Part 7
• WPC 2011/Part 15 (Lighthouses Battleships)