Draw a single, non-intersecting loop that only consists of horizontal and vertical segments between the dots. A number inside a cell indicates how many of the edges of that cell are part of the loop.
(Rules and example from PGP IB)
- Some cells may not be square-shaped and have four edges around them. (Irregular grids)
First appeared on 8th 24-Hour Puzzle Championship (2007). The author of the puzzle was Serkan Yürekli (Turkey).
Draw a single closed loop along the grid lines. The numbers that are outside the loop indicate the number of cell sides used by the loop. The numbers that are inside the loop indicate the number of the cell sides unused by the loop.
(Rules and example from WPC 2018 IB)
In the original puzzle by Serkan, the roles of inside and outside clues were the other way around. Commonly presented as an inside/outside Slitherlink variant, this puzzle is actually closer to shading puzzles (consider inside/outside patterns around clues).
Draw a closed loop along the dotted lines that uses each grid point at most once. A person walks along the loop, alternating between their left and right foot, always one edge per step. The numbers indicate how many steps on the edges of the respective cells that a person makes with their right foot.
(Rules and example from WPC 2019 IB)
First appeared on Puzzle Marathon contest on LMI in 2013. Author of the puzzle was Jakub Hrazdira (Czech Rep.)
Standard Slitherlink rules apply. However, exactly one number in each row and each column is wrong (value of that number doesn’t correspond with the number of square edges used by loop). Moreover, each square with the wrong number should be crossed by loop diagonally.
(Rules and example from 2013 Puzzle Marathon IB)
Draw a loop. Clues inside the loop work as Cave clues, while clues outside the loop work as Slitherlink clues.
(Example from WPC 2019 IB)
History of the puzzle
First appeared on Nikoli volume 26 (1989). The rule was suggested by 矢田レーニン ("Yada Renin"). Originally named スリザーリンク.
Originally the puzzle was presented like Bosnian Road. It took the current form when Nikoli merged the elements of a different puzzle called ナンピツ ("Nanpitsu," suggested by 轟由紀 ("Todoroki Yuki"), first appeared also in 1989).
Appearances in the past WPCs
- WPC 2019/Round 3 (Permaculture hybrid with Domino Hunt) by Silke Berendes
- WPC 2019/World Cup Round 1 (Hexagonal) by Roland Voigt
- WPC 2019/Round 4 by Roland Voigt
- WPC 2019/Round 8 (Classic, Standard (Inside) / Touching (Outside)) by Gabi Penn-Karras
- WPC 2019/Round 9 by Ulrich Voigt
- WPC 2019/World Cup Round 2 (Cave / Slitherlink) by Jürgen Blume-Nienhaus
- WPC 2019/Round 11 (Walking Slitherlink) by Christian Halberstadt
- WPC 2019/Team Playoffs by Roland Voigt
- WPC 2019/World Cup Playoffs by Gabi Penn-Karras
- WPC 2018/Round 4 (Hexagonal) by Jan Novotný
- WPC 2018/Round 4 (Cairo Pentagonal) by František Luskač
- WPC 2018/Round 7 by Jiří Hrdina
- WPC 2018/Round 13 (Liar Diagonal) by Petr Vejchoda
- WPC 2018/Round 13 (Knapp Daneben, Polygraph) by Jiří Hrdina
- WPC 2018/Individual Playoffs (Hexagonal, unused) by Jan Novotný
- WPC 2017/Round 1 (Coded) by Ashish Kumar
- WPC 2017/Round 5 (Irregular grid) by Prasanna Seshadri
- WPC 2017/Round 9 by Ashish Kumar
- WPC 2016/Round 2 by Matej Uher
- WPC 2016/Round 9 by Matúš Demiger