Einstein's riddle

This is the story behind Einstein's riddle: Albert Einstein supposedly created it in the late 1800s, and it is also said that he claimed 98% of the world population couldn't find a solution. In reality, it isn't that difficult, and I am not sure of the true origin, but I have seen this one floating around the internet, and it is a good brain exercise, so here it is:
- In a street there are five houses, painted five different colors.

- In each house lives a person of different nationality.

- These five homeowners each drink a different kind of beverage, smoke different brand of cigar and keep a different pet.

Einstein's riddle is: Who owns the fish?

Necessary clues:

1. The British man lives in a red house.
2. The Swedish man keeps dogs as pets.
3. The Danish man drinks tea.
4. The Green house is next to, and on the left of the White house.
5. The owner of the Green house drinks coffee.
6. The person who smokes Pall Mall rears birds.
7. The owner of the Yellow house smokes Dunhill.
8. The man living in the center house drinks milk.
9. The Norwegian lives in the first house.
10. The man who smokes Blends lives next to the one who keeps cats.
11. The man who keeps horses lives next to the man who smokes Dunhill.
12. The man who smokes Blue Master drinks beer.
13. The German smokes Prince.
14. The Norwegian lives next to the blue house.
15. The Blends smoker lives next to the one who drinks water.


The World's Hardest Riddle?

Some have claimed this to be the worlds hardest riddle. It isn't. It is a decent riddle, though, and a fun one for those who like riddles with systematic solutions. My own solution is below.

A chart seems like the most useful tool to help solve this riddle: Five columns for the five houses, and five rows for nationality, house color, type of drink, type of cigar, and finally, pets. Clue #8 states the man in the middle house drinks milk, so we can start by filling in that one of the 25 boxes created.

1st 2nd 3rd 4th 5th
Nation
Color
Drink Milk
Cigar
Pet

Then we deduce as much as possible from each clue as it becomes usable. The Norwegian living in the first house (# 9) could mean the first on the left or the right, since it isn't specified. I assume the left (first on chart) for now. Often, with riddles or puzzles, it is faster to make an assumption and if it doesn't work out go back and try the other way, rather than trying to hold open both possibilities while analyzing the other clues.

Clue# 14 says the Norwegian lives next to the blue house, so we can fill in the house color in the second column.

Clue # 4 says the green house is to the left of the white house, and #5 says it is occupied by a coffee drinker. The only place that works is in column four, so we can fill in color and drink there, and white for the color of the fifth.

Clue #1 says the British man is in the red house, and the third house is the only one that has neither color nor nationality specified yet, so we can fill in those two boxes. This also gives us the color of the first house, since only yellow is left. Yellow smokes Dunhill (#7), so we get that too.

Horses are next to the Dunhill smoker (#11). Put that in the second column and here we are so far:

1st 2nd 3rd 4th 5th
Nation Norwegian British
Color Yellow Blue Red Green White
Drink Milk Coffee
Cigar Dunhill
Pet Horses

I have to admit that I was stumped at this point, until I started looking for "clumps" of information. The idea is that if you can put three or more things together at this point, there is likely only one column they will fit in. In this case, I started with clue # 12: The man who smokes Blue Master drinks beer. That is two bits of information that go together.

Now we have to determine what other bit of information can be "attached" to that. From what we have on the chart, we can see that the Norwegian smokes Dunhill and the British man drinks milk, so we rule out two nationalities.# 13 says the German smokes Prince, and #3 says the Danish man drinks tea, so we are left with just the Swedish man, who we now know smokes Blue Master and drinks beer. Scanning the clues for more information about the Swedish man we see that he has dogs (# 2). The only place that these four items fit is column five, so we fill that in.

Now it gets a bit easier. The "Blends" smoker is next to a water-drinker (#15) and the cat owner (# 10), which fits only in house 2 now, so we can put "blends" in 2 and "water" in 1. That leaves only "tea" for 2. Clue # 3 says the Danish man drinks tea, so we get that as well, which leaves just one slot (house 4) for the German.

The German smokes Prince (#13), which leaves only one slot (house 3) for the Pall Malls. This is how the chart now looks:

1st 2nd 3rd 4th 5th
Nation Norwegian Danish British German Swedish
Color Yellow Blue Red Green White
Drink Water Tea Milk Coffee Beer
Cigar Dunhill Blends Pall Mall Prince Blue Master
Pet Horses Dogs

Clue # 6 says the person who smokes Pall Mall rears birds (house 3). Clue #10 says the man who smokes Blends lives next to the one who keeps cats, so "cats" can only fit in the house 1 column. That leaves but one slot open, so the coffee-drinking, Prince Cigar-smoking German in the green house owns the fish in Einstein's riddle.

This is my own way of figuring it out, and I am sure there are other ways to arrive at the answer. It is a fun puzzle, and particularly good for practicing logical reasoning. This makes it worthy of our time whether or not this is truly Einstein's riddle.