Dfs

hashiwokakero (“build bridges”, nikoli) hands you a grid of numbered islands and asks you to join them with bridges until every number is spent. it is the friendliest possible introduction to constraint satisfaction: the constraints are few and visual, propagation alone solves most human-published puzzles, and when it doesn’t, you get to write a backtracking search. this page documents my solver at code/private/hashi/ — a go rewrite of a uni assignment originally in c — including the debugging session that writing this page forced on it. 𐃏

Personal Motivations#

I grew up as a child with this puzzle in my house. My mother could solve it, along with a couple members on her side of the family.

Mum never knew the algorithm, nor any techniques beyond “My hand just knows”; as a result I spent 4 determined days in my youth working it until I had solved it.