The zebra puzzle is a well-known
logic puzzle
A logic puzzle is a puzzle deriving from the mathematics, mathematical field of deductive reasoning, deduction.
History
The logic puzzle was first produced by Charles Lutwidge Dodgson, who is better known under his pen name Lewis Carroll, the au ...
. Many versions of the puzzle exist, including a version published in ''
Life International'' magazine on December 17, 1962. The March 25, 1963, issue of ''Life'' contained the solution and the names of several hundred successful solvers from around the world.
The puzzle is often called Einstein's Puzzle or Einstein's Riddle because it is said to have been invented by
Albert Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
as a boy; it is also sometimes attributed to
Lewis Carroll
Charles Lutwidge Dodgson (; 27 January 1832 – 14 January 1898), better known by his pen name Lewis Carroll, was an English author, poet and mathematician. His most notable works are ''Alice's Adventures in Wonderland'' (1865) and its sequel ...
.
[
][
] However, there is no known evidence for Einstein's or Carroll's authorship and the ''Life International'' version of the puzzle mentions brands of cigarette, such as
Kools, that did not exist during Carroll's lifetime or Einstein's boyhood.
The Zebra puzzle has been used as a
benchmark
Benchmark may refer to:
Business and economics
* Benchmarking, evaluating performance within organizations
* Benchmark price
* Benchmark (crude oil), oil-specific practices
Science and technology
* Benchmark (surveying), a point of known elevati ...
in the evaluation of computer algorithms for solving
constraint satisfaction problem
Constraint satisfaction problems (CSPs) are mathematical questions defined as a set of objects whose state must satisfy a number of constraints or limitations. CSPs represent the entities in a problem as a homogeneous collection of finite constra ...
s.
Description
The following version of the puzzle appeared in ''Life International'' in 1962:
Solution
Assuming that one person drinks water and one owns a zebra, then it is possible not only to deduce the answers to the two questions, but to figure out a complete solution of who lives where, in what color house, keeping what pet, drinking what drink, and smoking what brand of cigarettes. By considering the clues a few at a time, it is possible to slowly build inferences that incrementally complete the puzzle's unique correct solution. For example, by clue 10, the Norwegian lives in house #1, and by clue 15, house #2 must be blue. The Norwegian's house therefore cannot be blue, nor can it be red, where the Englishman lives (clue 2), or green or ivory, which are next to each other (clue 6). It must therefore be yellow, which means the Norwegian also smokes Kools (clue 8).
The March 25, 1963 issue of ''Life International'' contained the following solution, and the names of several hundred solvers from around the world.
Alternate solution
Clue 10 mentions the "first" house, without specifying whether it is the house on the extreme left or extreme right if standing in front of them. However, selecting either side as the first house does not change the outcome as to who drinks the water and who has the zebra.
Other versions
Other versions of the puzzle have various differences from the ''Life International'' puzzle, in which various colors, nationalities, cigarette brands, drinks, and pets are substituted,
or the clues are given in a different order. These do not change the logic of the puzzle.
A slightly simplified version of this puzzle appears in the video-game ''
Dishonored 2
''Dishonored 2'' is a 2016 Action-adventure game, action-adventure video game developed by Arkane Studios and published by Bethesda Softworks for Microsoft Windows, PlayStation 4, and Xbox One. It is the sequel to 2012's ''Dishonored''. After ...
'' , where the player character has to solve it to unlock a gate to an abandoned mansion.
Some versions of the puzzle indicate that the green house is on the left of the ivory house, instead of on the right of it.
This results in swapping the two corresponding houses with all their properties, and makes the puzzle easier to solve.
References
Notes
{{notelist
External links
corresponding entryon
Opencog
OpenCog is a project that aims to build an open source software, open source artificial intelligence framework. OpenCog Prime is an architecture for robot and virtual embodied cognition that defines a set of interacting components designed to giv ...
's wiki
programming task on Rosetta codeSolvable Puzzleon Brainzilla
Alloy Model for this puzzleWatson
Logic puzzles
Albert Einstein
1962 works