Well, this is how I worked it out. And, of course, it might be all wrong. But, anyway, after days of working on it and walking through a dense fog, this is what I managed to do:

First things first. There are too many colours, too many drinks, too many pets, and too many cigars for my liking. Let me list them out. The colours of the houses mentioned are yellow, blue, red, green, and white. The drinks mentioned in the hints are water, tea, milk, coffee, and beer. The nationalities mentioned are British, Swede, Dane, Norwegian, and German. The pets mentioned are dogs, birds, cats, and horses. There is no mention of fish in the hints, but the question abruptly posed is: Who keeps fish? So, I take it that the fifth pet is fish. Finally, the cigar brands mentioned are Dunhill, Blend, Blue Master, Prince, and Pall Mall. Phew! That was enough work for me!

I have also assumed that the houses are in a single row since there is mention of the first house, and also about a house being on the left of another.

Ah good! Now I can conjure up an image of five houses in five different colours standing in a row. So, let me call the houses: First House, Second House, Third House, Fourth House, and Fifth House.

Hint number 9 tells me that the Norwegian lives in the First House. Hint number 8 tells me that the man living in the house right in the center drinks milk. The house right in the centre is, of course, the Third House. Hint number 14 says the Norwegian lives next to the blue house; since the Norwegian lives in the First House, the house next to his is the second one and, so, the Second House is blue. I think I am getting somewhere. Let me tabulate what I have learned so far:

Clues 4 and 5 state that the green house is on the left of the white house, and that the green house owner drinks coffee. These clues had me tearing my hair out because I just could not figure out which house is on the left and which on the right. Anyway, I consider myself facing the houses (not with my back to them) in order to determine the left and right houses. In that case, the First House has no house on its left and, so, it cannot be the white house. It cannot be green because it is on the left of the blue house (the Second House). The green house can be the Third House and in that case the Fourth House will be white. The green house can be the Fourth House and in that case the Fifth House will be white. The Fifth House cannot be green because the Fifth House, being the last in the row, is not on the left of any house. So, the green house is either the Third House or the Fourth House, and the white house is either the Fourth House or the Fifth House.

The very first hint says the British lives in a red house. The First House cannot be red because it is occupied by the Norwegian. The Second House is blue. The Third House can be red. The Fourth House cannot be red because then the green and white houses will not be next-door to each other as the hint requires. The Fifth House can be red. So, the red, green and white houses have to be between the Third House, Fourth House and the Fifth House. The Second House is blue. Therefore, the First House has to be yellow and it is occupied by the Norwegian. Clue number 7 states the owner of the yellow house smokes Dunhill. So, the Norwegian smokes Dunhill.

Let me once again list out the definite findings:

Clue number 11 says "The man who keeps horses lives next to the man who smokes Dunhill". The Norwegian smokes Dunhill and the house next to his is the blue house. So, the blue house owner keeps horses. Let me record this instantly.

We have accounted for the yellow and blue houses which are the First House and the Second House respectively. That leaves us with the red, green and white houses. Clue 5 says "The green house owner drinks coffee". The green house, therefore, cannot be the Third House because its owner drinks milk. We have already seen that the green house is either the Third House or the Fourth House. But, now, the Third House has been ruled out. So, the Fourth House is green. The Fifth House is, therefore white. That leads to the conclusion that the Third House is red which is occupied by the British. Clue 5 states that the green house owner drinks coffee. Let me record these findings immediately.

Clue 2 says, "The Swede keeps dogs as pets". The First House is occupied by the Norwegian, the Second House owner keeps horses, while the Third House owner is British. Therefore, the Swede occupies either the Fourth House or the Fifth House.

Clue 3 states, "The Dane drinks tea". The First House is occupied by the Norwegian, the Third House owner is British, while the Fourth House owner drinks coffee. Therefore the Dane occupies either the Second House or the Fifth House.

Hint number 12: The owner who smokes Blue Master drinks beer. The Norwegian smokes Dunhill, the British drinks milk, and the Fourth House owner drinks coffee. Therefore, the Blue Master smoker and beer drinker must occupy either the Second or the Fifth house. The Dane we have already seen can occupy either the Second or the Fifth House. Therefore, if the Dane occupies the Second House, then the Blue Master smoker and beer drinker occupies the Fifth House, and vice versa. Hint 13: The German smokes Prince. He is of course not a Norwegian (First House), not a British (Third House), not a Dane (Second or Fifth House), and doesn't smoke Blue Master (Second or Fifth house). The only option then is that the German occupies the Fourth House. We have also seen that the Swede can occupy the Fourth or the Fifth House. But since the German lives in the Fourth House, it implies that the Swede, who keeps dogs, lives in the Fifth House. This leaves the Second House for the Dane who drinks tea. It is the Swede, therefore, who smokes Blue Master and drinks beer. Let's record these facts immediately.

We have accounted for the Dunhill, Blue Master and Prince smokers. The Pall Mall and Blend smokers therefore have to be between the Dane and the British. Clue number 15 says, "The man who smokes Blend has a neighbor who drinks water". The British has neighbours who drink tea and beer; so he can't be the Blend smoker. The British, thus, smokes Pall Mall and the Dane smokes Blend. Hint number 6: The person who smokes Pall Mall rears birds. It is therefore the British who rears birds. Let's record these facts immediately.

We get back to clue number 15: The man who smokes Blend has a neighbour who drinks water. The Dane smokes Blend and he has the Norwegian and the British as his neighbours. The British drinks milk; so, it is the Norwegian who drinks water. Clue number 10: The man who smokes Blend lives next to the one who keeps cats. The Dane is a Blend smoker and he lives next to the Norwegian and the British. The British rears birds and, so, it is the Norwegian who keeps cats. That leaves only the fish and the German. It is, therefore, the German who keeps fish. Let's record these facts at once.

I think I will go for a stroll!!!!