Brain Teasers
One Seat in the Boat
The wolf, goat and cabbage river crossing as a story - seven crossings, one backward move.
How it works
A farmer must ferry a wolf, a goat and a sack of cabbages across a river in a boat that holds him plus one passenger. Left unsupervised, the wolf eats the goat and the goat eats the cabbages; the wolf has no interest in cabbage. He may cross as often as he likes in either direction. The story asks how he gets all three across intact. You lock in a guess, then step through the answer and breakdown.
How scoring works
No grading - your guess is displayed back beside the answer. The story teasers share one lifetime unlock for free users.
The key insight
The goat appears in both conflicts while the wolf and cabbage are safe together, so the goat crosses first and can never be left with either of the others. Keeping that invariant true mid-puzzle forces the non-obvious move: after delivering the wolf, the farmer brings the goat back. Seven crossings total, and the lesson is that progress in a constrained search is not monotone - the 'no backward moves' rule is one solvers invent themselves.
The full step-by-step solution lives at /brain-teasers/river-crossing/solution.
A worked example
Goat over, back empty, wolf over, goat BACK, cabbage over, back empty, goat over - seven crossings. Taking the cabbage third instead of the wolf works symmetrically; refusing to let anything ride back never works.
Common mistakes
• Assuming each passenger crosses exactly once - the rule that makes the puzzle look impossible is one you added yourself.
• Searching moves at random instead of identifying the goat as the piece in every conflict.
• Declaring it unsolvable after three moves instead of questioning the invented constraint.
Why interviews test this
As an interview question this is a state-space search in disguise: interviewers listen for the invariant - the goat never unsupervised with anything - not a memorised sequence. The written solution is at /brain-teasers/river-crossing/solution.