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 2010 24hPC IB)
- 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
Later, "Retrograde Penta" appeared on WPC 2003/Part 2. Its author is currently unknown.