Who Owns the Zebra?
Solution

The solution can be summarized in the following table:

Solution to Who Owns the Zebra?

House #1	House #2	House #3	House #4	House #5
Norwegian	Ukrainian	Englishman	Spaniard	Japanese
Yellow	Blue	Red	Ivory	Green
Fox	Horse	Snails	Dog	Zebra
Kools	Chesterfields	Old Gold	Lucky Strikes	Parliament
Water	Tea	Milk	Orange Juice	Coffee

To get the solution, I filled in all the obvious data. This still left me with lots of clues that I couldn't easily analyze. However, my table of results had a simple choice: Japanese or Ukrainian in house number 2. Putting the Japanese there quickly led to problems; with the Ukrainian there I was able to proceed. I reached another impasse, and had to choose between having the green house in position 4 or 5. Again, after some thought, position 4 was impossible, and with the green house in position 5, the solution is quickly reached.

The zebra puzzle has become a useful example for certain kinds of constraint satisfaction problems. See, for instance:

• Rina Dechter,
  Enhancement Schemes for constraint processing: Backjumping, learning, and cutset decomposition,
  Artificial Intelligence,
  Volume 41, Number 3, January 1990, pages 273-312.

Back to Who Owns the Zebra.