Retrograde Battleships

Rules

Possible placements of the Battleships fleet is given. Ships are oriented horizontally or vertically and they don't touch each other, not even diagonally. There cannot be any ship segments on water marks.

(Rules and example (standard fleet of size 3) from the 11th 24hPC IB)

Rule variations

• Instead of placing 1-by-n rectangles, placing any set of given polyominoes can theoretically work. (Compare Battleships and Pentominoes) For example, when the given set is a full set of 12 pentominoes, this puzzle is alternatively called "Retrograde Pentominoes".

History of the puzzle

First appeared on WPC 2000/Part V, Battleships variations round. The author of the puzzle was Erich Friedman (USA).

Later, "Retrograde Penta" appeared on WPC 2003/Part 2. Its author is currently unknown.

Appearances in the past WPCs

• WPC 2016/Round 8 (Pentominoes) by Matúš Demiger
• WPC 2003/Part II (Pentominoes)
• WPC 2000/Part V by Erich Friedman.