Draw a closed loop into the grid that runs horizontally and vertically and passes through each cell at most once. The loop must enter and leave each region at least twice. For multiple visits of the same region, each visit must pass through the same number of cells. That number can be equal or different for different regions. If a region contains a number, that number indicates how many cells in that region are not used by the loop. Grey cells cannot be used by the loop, and they are not part of any region.
(Rules and example from WPC 2019 IB)
History of the puzzle
Appeared on WPC 2019/Round 12, an "innovations" round. The puzzles were written by Erhard Notz.
Appearances in the past WPCs
- WPC 2019/Round 12 by Erhard Notz