Einstein's puzzle is a well-known logic puzzle. A logic puzzle is a puzzle deriving from the mathematics field of deduction. ...

It is often called Einstein's Puzzle or Einstein's Riddle because it is said to have been invented by Albert Einstein as a boy. A common claim attached to this puzzle is that Einstein said "only 2 percent of the world's population can solve this," although there is no known source for such a quote, or for Einstein's authorship. Albert Einstein photographed by Oren J. Turner in 1947. ...

There are several version of this puzzle. Some ask "Who owns the fish?" instead of "Who owns the zebra?" The version below is quoted from the first known publication in Life International magazine on December 17, 1962. The May 25, 1963 issue contained the solution given below and the names of several hundred solvers from around the world. December 17 is the 351st day of the year (352nd in leap years) in the Gregorian Calendar. ... 1962 (MCMLXII) was a common year starting on Monday (link will take you to calendar). ... May 25 is the 145th day of the year in the Gregorian calendar (146th in leap years). ... 1963 (MCMLXIII) was a common year starting on Tuesday (link will take you to calendar). ...

The original puzzle

1. There are five houses.
2. The Englishman lives in the red house.
3. The Spaniard owns the dog.
4. Coffee is drunk in the green house.
5. The Ukrainian drinks tea.
6. The green house is immediately to the right of the ivory house.
7. The Old Gold smoker owns snails.
8. Kools are smoked in the yellow house.
9. Milk is drunk in the middle house.
10. The Norwegian lives in the first house.
11. The man who smokes Chesterfields lives in the house next to the man with the fox.
12. Kools are smoked in the house next to the house where the horse is kept.
13. The Lucky Strike smoker drinks orange juice.
14. The Japanese smokes Parliaments.
15. The Norwegian lives next to the blue house.

Now, who drinks water? Who owns the zebra?

In the interest of clarity, it must be added that each of the five houses is painted a different color, and their inhabitants are of different national extractions, own different pets, drink different beverages and smoke different brands of American cigarettes. One other thing: In Statement 6, right means your right. In Statement 11, next means to ""your"" left.

An important point not mentioned in the original publication was that the houses are in a row and ordered from left to right. Note also that it is possible not only to deduce the answers to the two questions but to figure out who lives where, in what color house, keeping what pet, drinking what drink and smoking what brand of cigarettes.

Solution

Of course, this solution makes the assumption that after the other four pets and four drinks have been found, the missing ones are a zebra and water, which is never specified. Some people maintain that the only correct answer is that we can't answer the question with the information given, because it's possible there is no zebra and no water anywhere.

External links

• An SWI Prolog Solution to Einstein's Puzzle
• Who owns the fish? A Common Lisp solution to "Einstein's Riddle", includes C++ solutions
• Einstein's Riddle in C# (Knowing.NET - link does not work in Firefox)