Hebi-Ichigo

Rules

Write numbers from 1 and 5 into some white cells to build sequences of orthogonally adjacent cells, containing all numbers in strictly increasing or decreasing order. The chain of numbers denotes a snake.

No two snakes can touch each other orthogonally, but they can touch diagonally.

Numbers in clue cells denote which number in a black cell (number cell) is the first number in the direction the arrow points to. A zero denotes that there is no number cell in the direction the arrow points to, up to the edge of the grid or the nearest black cell (whichever is closer).

No snake may see another snake. A snake's eyes are on the side of its head (the 1-cell) opposite the 2-cell. It can only see in that direction, in a straight line, up to the edge of the grid or the nearest black cell (whichever is closer).

(Rules (modified) from WPC 2016 IB, example by EctoPlasma)

History of the puzzle

First appeared on Nikoli volume 126 (2009). Invented by あるかり工場長 (Alkali Kojocho). Hebi-Ichigo is a genus of strawberry native to South-east Asia. Furthermore, it is a pun; Ichigo corresponds to 1 and 5 (ichi and go in Japanese).

Appearances in the past WPCs

• WPC 2016/Round 17 by Matej Uher