# Solving a Zebra Puzzle using Prolog

In this challenge, we are aiming to get the computer to solve Zebra Puzzles by creating Prolog programs.

#### Zebra Puzzle?

Zebra Puzzles, also known as Einstein’s Riddles, are a type of logic puzzles where you have to use the clues to make logic deductions in order to solve a given problem.

Our zebra puzzle will be based on the following scenario:

Three kids went to a superheroes fancy dress birthday party.
The names of the three kids are Ethan, Ali and Anya.
They dressed up as Spiderman, Captain America and Iron Man.
The kids are 6, 8 and 10 years old.

We don’t know how each kid dressed up or how old each kid is but we have the following clues:

• Anya was dressed up as Spiderman.
• Ethan was not dressed up as Captain America.
• The youngest kid dressed up as Spiderman.
• The kid who is 8 years old dressed up as Captain America.

You can solve this puzzle manually using the following grid:

#### Prolog?

Prolog is a declarative language that uses a recursive approach to solve logic puzzles. To solve a logic Puzzle using Prolog, a programmer first needs to declare a knowledge base consisting of a collection of facts and rules. This knowledge base can then be used to run queries to try to solve the puzzle.

#### Setting up the knowledge base

Let’s first focus on declaring the key facts of our puzzle as follows:

```/* Facts */
kid(ethan).
kid(ali).
kid(anya).

hero(spiderman).
hero(captain_america).
hero(iron_man).

age(six).
age(eight).
age(ten).```

We will then implement our clues as rules:

```relation(K,H,A):- K=anya, H=spiderman, age(A).
relation(K,H,A):- K=ethan, hero(H), age(A), H\=captain_america.
relation(K,H,A):- kid(K), H=spiderman, A=six.
relation(K,H,A):- kid(K), H=captain_america, A=eight.```

We will add two extra rules that will be used to solve this puzzle and to reinforce the fact that two kids cannot have the same age or the same costume.

```different(X,Y,Z):-X\=Y,X\=Z,Y\=Z.
solve(K1,H1,A1,K2,H2,A2,K3,H3,A3):- relation(K1,H1,A1),relation(K2,H2,A2),relation(K3,H3,A3),different(K1,K2,K3),different(H1,H2,H3),different(A1,A2,A3).
```

#### Solving the puzzle…

We have created this knowledge base using an online Prolog Environment called Swish:
https://swish.swi-prolog.org/p/Superheroes%20Zebra%20Puzzle.pl

You can now run the following query to solve this puzzle:

`?-solve(K1,H1,A1,K2,H2,A2,K3,H3,A3)`

Pick up any Logic Grid Puzzle from this website and build your own set of facts and rules in Prolog to solve your puzzle.

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