Blacken some white cells and then draw a single closed loop (without intersections or crossings) through all remaining white cells. Loop paths must be orthogonal. Blackened cells cannot share an edge with each other. Some cells are outlined and in gray and cannot be part of the loop. Numbered arrows in such cells indicate the total number of blackened cells along the direction of the arrow, starting in the arrowed cell and going along a row or column to the edge of the grid.
(Rules and example from PGP IB)
History of the puzzle
First appeared on Nikoli volume 86 (1999). Invented by 天歩 ("Tenpo"). The name ヤジリン ("Yajilin") is formed from a contraction of two words, 矢印 ("yajirushi," "arrow") and リング ("ring").
The concept of arrows combined with numbers derives from an earlier puzzle Yajisan Kazusan.
Invented by Naoki Inaba (Japan) under the name ブロックボックス (Block Box). First appeared in 2005.
The name Regional Yajilin was given by Prasanna Seshadri (India) when he independently invented it in 2012 and this name was popularised after Borders & Beyond contest on Logic Masters India. Consequently this puzzle is known as a Yajilin variant, despite the lack of arrows (Yaji part of the name).
Shade in some cells. Shaded cells are not allowed to be orthogonally adjacent. Draw a closed loop that passes through all the remaining cells. A number in a region indicate the number of shaded cells in that region.
(Rules from Borders & Beyond IB, example from Naoki Inaba's website)
First appeared on 2016 Polish Nationals. Author of the puzzle was Prasanna Seshadri (India).
Blacken some white cells and draw a closed loop passing through centres of all remaining white cells horizontally or vertically. Blackened cells cannot share an edge with each other. The loop can pass through clue cells, and clue cells that are not passed through must be blackened. Numbered arrows in white cells indicate the total number of blackened cells in the direction pointed at by the arrow. Numbers in blackened clue cells do not necessarily have to be satisfied.
(Rules and example from WPC 2017 IB)
Appearances in the past WPCs
- WPC 2019/Round 9 by Ulrich Voigt
- WPC 2019/World Cup Round 3 by Gabi Penn-Karras
- WPC 2019/World Cup Playoffs by Roland Voigt
- WPC 2018/Round 7 by Jiří Hrdina
- WPC 2018/Round 11 (Regional Yajilin) by Jan Zvěřina
- WPC 2018/Team Round 3 (part of a combination puzzle) by Jiří Hrdina
- WPC 2018/Individual Playoffs (Regional Yajilin, unused) by Jiří Hrdina
- WPC 2017/Round 3 by Ashish Kumar
- WPC 2017/Round 4 (Transparent Yajilin) by Prasanna Seshadri
- WPC 2017/Round 10 ("Optimizer") by Ashish Kumar
- WPC 2016/Round 2 by Matej Uher
- WPC 2016/Round 14 (part of a Permaculture hybrid) by Matúš Demiger
- WPC 2015/Round 2 by Gabriele Simionato
- WPC 2015/Round 11
- WPC 2015/Round 12
- WPC 2014/Round 3
- WPC 2014/Round 6
- WPC 2014/Round 10
- WPC 2013/Part 2
- WPC 2013/Part 6 (Yajilin, Doubled Yajilin)
- WPC 2012/Part 10
- WPC 2011/Part 9