HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION
COLOR
DRINK
CIGAR
PET

This is the way I solved the problem. There are probably other ways, too. You should check to make sure I got this right.

There are five houses. For each house, there are five bits of information about the house and its occupant: the house's color and the occupant's nationality, pet, favorite drink, and favorite cigar.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway
COLOR
DRINK
CIGAR
PET

Fact 9: The Norwegian lives in the first house.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway
COLOR		blue
DRINK
CIGAR
PET

Fact 14: The Norwegian lives next to the blue house.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway
COLOR		blue
DRINK			milk
CIGAR
PET

Fact 8: The man living in the house right in the center drinks milk.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway
COLOR		blue		green	white
DRINK			milk	coffee
CIGAR
PET

Fact 4: The green house is on the left of the white house.

This means the green and white houses are next to each other with the green on the left. As I'm writing this, I'm realizing that this is open to interpretation though -- maybe it just means that if you look at the five houses, the green one is to the left of the white one. But I can defend my choice with a quick piece of logic: my choice leads to only one solution. If my interpretation of the words is incorrect, my choice is still consistent with the more general interpretation. If the more general interpretation has only one solution, it must be mine. If the more general interpretation allows for more than one solution, then the problem would be indeterminate; since the problem implicitly claims to have a unique solution, this would be inconsistent. Thus I like my choice of interpretation.

Fact 5: The green house owner drinks coffee.

Together these two facts mean we have to fit a piece that looks like:

green	white
coffee

into the second two rows of the table. The only place it can fit is the fourth and fifth columns.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway		Britain
COLOR		blue	red	green	white
DRINK			milk	coffee
CIGAR
PET

Fact 1: The Brit lives in a red house.

This means we have to fit a piece that looks like:

Britain

red

into the first two rows of the table. The only place it can fit is the third column.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway		Britain
COLOR	yellow	blue	red	green	white
DRINK			milk	coffee
CIGAR
PET

The only place left for ``yellow'' is the first column.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway		Britain
COLOR	yellow	blue	red	green	white
DRINK			milk	coffee
CIGAR	Dunhill
PET		horses

Fact 7: The owner of the yellow house smokes Dunhill.

Fact 11: The man who keeps horses lives next to the man who smokes Dunhill.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway		Britain
COLOR	yellow	blue	red	green	white
DRINK			milk	coffee
CIGAR	Dunhill
PET		horses

Next comes a teensy bit of brute force.

We have three nationalities (German, Swede, and Dane) to put in three columns. Absent any further analysis, there are six ways to do so. However, we can use facts 2 and 3 to pare the list to just three ways.

For the heck of it, let's place the German first.

Suppose the German lives in house #2. Fact 3 tells us the Dane drinks tea so he cannot live in house #4. Thus the Swede is in house #4 and the Dane in #5.

Suppose the German lives in house #4. Fact 2 tells us the Swede keeps dogs as pets so he cannot live in house #2. Thus the Dane is in house #2 and the Swede in #5.

Suppose the German lives in house #5. Fact 3 tells us the Dane drinks tea so he cannot live in house #4. Thus the Dane is in house #2 and the Swede in #4.

We can also throw in fact 13 that the German smokes Prince cigars. All three possibilities are shown on the next page.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Germany	Britain	Sweden	Denmark
COLOR	yellow	blue	red	green	white
DRINK			milk	coffee	tea
CIGAR	Dunhill	Prince
PET		horses		dogs

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee
CIGAR	Dunhill			Prince
PET		horses			dogs

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Sweden	Germany
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee
CIGAR	Dunhill				Prince
PET		horses		dogs

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Germany	Britain	Sweden	Denmark
COLOR	yellow	blue	red	green	white
DRINK			milk	coffee	tea
CIGAR	Dunhill	Prince
PET		horses		dogs

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee	beer
CIGAR	Dunhill			Prince	Blue Master
PET		horses			dogs

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Sweden	Germany
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee
CIGAR	Dunhill				Prince
PET		horses		dogs

Next we'll look at fact 12: the owner who smokes Blue Master drinks beer. That means we need to fit the piece:

beer

Blue Master

into the third and fourth rows of the table. It can't fit into the first or third tables; we can toss them as possibilities.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee	beer
CIGAR	Dunhill			Prince	Blue Master
PET		horses			dogs

This brings us to the above; only clues 6, 10, and 15 are left.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK		tea	milk	coffee	beer
CIGAR	Dunhill		Pall Mall	Prince	Blue Master
PET		horses	birds		dogs

Clue 6 says that the person who smokes Pall Mall raises birds. That means we need to fit the piece:

Pall Mall

birds

into the last two rows of the table. Only the third column is a possibility.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK	water	tea	milk	coffee	beer
CIGAR	Dunhill	Blend	Pall Mall	Prince	Blue Master
PET	cats	horses	birds		dogs

Clue 10 says we need the person who smokes Blend next to the one who keeps cats, and clue 15 says he also lives next to the person who drinks water (not necessarily the same one who keeps cats). We need one of the pieces:

water

water

water

water

Blend

or

Blend

or

Blend

or

Blend

cats

cats

cats

cats

in the last three rows of the table. Only the set of cells on the left offers a possibility.

	HOUSE #1	HOUSE #2	HOUSE #3	HOUSE #4	HOUSE #5
NATION	Norway	Denmark	Britain	Germany	Sweden
COLOR	yellow	blue	red	green	white
DRINK	water	tea	milk	coffee	beer
CIGAR	Dunhill	Blend	Pall Mall	Prince	Blue Master
PET	cats	horses	birds	fish	dogs

That's all the clues. The only spot left is the pet that the German keeps: fish!