Find a path through the grid that runs horizontally and vertically, starts and ends in the black circle, and passes through each cell except those with numbers exactly once.
Along the path, a traveler passes through several grey cells. To be allowed to do so, they must have a permit A 38 which will be obtained in cells horizontally, vertically and diagonally neighbouring to cells with numbers. The clue numbers refer to the order in which all neighbouring cells are visited; for each clue number N, a permit will be obtained in the Nth neighbouring cell in this order. For example, if a clue cell contains numbers 2 and 5, permits will be obtained in the 2nd and 5th neighbouring cell along the path. Permits cannot be obtained in grey cells.
When traveling through a grey cell, the traveler must have exactly one permit which is then revoked; in other words, the traveler must alternately obtain and use the permits.
(Rules and example from WPC 2019 IB)
History of the puzzle
Invented by Erhard Notz (Germany) and first appeared on LMD Portal in 2016.
"Passierschein A38" is a stock phrase in German meaning "an imaginary permit that is impossible to get," according to Wiktionary. Derived from 1976 animated film The Twelve Tasks of Asterix.
Appearances in the past WPCs
- WPC 2019/Round 2 by Erhard Notz