# Dissecting Zebra Puzzle (Puzzle building)

The zebra puzzle tasks you with finding the person with the zebra and the person who drinks water from a row of 5 houses. The clues are built such that they do not mention either zebra or water but still reveal where everything is. This is ensured by pointing out that everything is different in every house.

The clues in the puzzle take three forms.

The first kind of clues are direct. They immediately tell where something is. You can immediately fill out where something is, and eliminate it as a choice elsewhere.

The second kind of clues tell that two different properties appear together. These make the majority of the puzzle. These allow you to drop other if the another cannot appear in a house. They also allow you to insert another if the other is determined.

The third kind of clue tell that the one property appears next to the another. They behave similar to the second kind of clues, except that they chain properties in the adjacent houses together.

Every rule eliminate possibilities and can be used for propagating constraints. For example, knowing that kools are smoked in the yellow house and that kools are smoked next to horse house allow you to determine that the horse is next to the yellow house.

Knowing that something cannot appear anywhere else allow you to fill it into where it appears. This happens naturally because you cannot solve the puzzle if everything does not appears somewhere. In fact, this is the distinct feature for this kind of puzzles. The last step in solving the puzzle must arrive through isolation because the zebra and water do not appear anywhere in the clues.

Eventually you may have to guess in this kind of a puzzle. Before doing the guess mark every cell that you found out by deduction. This allows you to backtrack and do a different decision in the case that the guess does not yield a solution. Also mark the guesses in the order that you did them. When you hit a dead end do not erase your memo. At least on the bare minimum keep the track of the false guesses you did, and note that a false guess is the total of all the guesses you did.

Now lets consider what you need to know in order to build this kind of a puzzle yourself. You have to know how to find every solution to your puzzle. It involves doing every guess and checking on whether the answer to the puzzle is unique, given all the constraints you tell to the solver.

If the answer to the puzzle is unique, then you've got a new puzzle. Once you have one puzzle, you can further refine it to make it harder. A rough difficulty level can be determined by how many times you have to guess in order to solve the puzzle.

Now you have one way to create this kind of a puzzle on your own. It may not be the most efficient, neatest or even well-defined way to create new puzzles. It gives a starting point though.