Shade some cells black (leaving the other cells white) such that all shaded cells are connected orthogonally into a single region. All non-shaded cells must be connected orthogonally (through other non-shaded cells) to the edge of the grid. No 2×2 group of cells can be entirely shaded black.
The numbers to the left of (and above) the main grid represent the lengths of contiguous blackened cell blocks in the corresponding row (or column). The lengths are not necessarily given in order from left to right (or top to bottom), and cell blocks must contain at least one unblackened cell between them. As a special case, if the single clue “0” is given, it means there should be no blackened cells in that row (or column).
(Rules and example from PGP IB)
- In some puzzles, some numbers are replaced with question marks.
- Coral with Question Marks: a puzzle in WPC 2018/Round 13. Clues are in the correct order. Every clue that are not 2 are replaced with question marks.
History of the puzzle
Invented by Zoltán Horváth (Hungary) in 2001, according to his blog.
Appearances in the past WPCs
Listed here are appearances of classic to almost-classic Coral. For variants, see list of Coral variants#Appearances in the past WPCs.
- WPC 2019/World Cup Playoffs by Rainer Biegler
- WPC 2018/Round 1 by Jiři Hrdina
- WPC 2018/Round 13 (Coral with Question Marks, Coded Coral) by Jiří Hrdina
- WPC 2018/Team Round 2 (Hexagonal, part of a hybrid) by Jiří Hrdina
- WPC 2017/Round 3 by Ashish Kumar
- WPC 2017/Round 10 ("Optimizer") by Prasanna Seshadri
- WPC 2015/Round 2
- WPC 2012/Part 5
- WPC 2011/Part 4 ("Borderless")
- WPC 2011/Part 12