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https://github.com/ashawley/nqueens-scala
N-Queens problem
https://github.com/ashawley/nqueens-scala
Last synced: 5 days ago
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N-Queens problem
- Host: GitHub
- URL: https://github.com/ashawley/nqueens-scala
- Owner: ashawley
- License: gpl-3.0
- Created: 2019-03-04T12:26:11.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2019-12-17T12:36:30.000Z (about 5 years ago)
- Last Synced: 2024-10-31T12:46:48.445Z (about 2 months ago)
- Language: Scala
- Homepage: https://ashawley.github.io/nqueens-scala/2.13.0-M5/api/
- Size: 958 KB
- Stars: 1
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
N-Queens problem in Scala
============================
[](https://ci.appveyor.com/project/ashawley/nqueens-scala)
[](https://circleci.com/gh/ashawley/nqueens-scala)
[](https://travis-ci.org/ashawley/nqueens-scala)
Problem: Place ''N'' queens on a board so no queen threatens another queen.
_|_|_|_|_|Q|_|_
_|_|_|Q|_|_|_|_
_|_|_|_|_|_|Q|_
Q|_|_|_|_|_|_|_
_|_|_|_|_|_|_|Q
_|Q|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
_|_|Q|_|_|_|_|_
Solving the problem for a 8 queens:
```scala
NQueens.solve(8)
```
It's possible to solve for other board sizes:
decimal.
```scala
NQueens.solve(10) // 10 queens on a 10-by-10 board.
```
### Overview
This solution is written in [Scala] 2.12 and only depends on the Scala
standard library, and [Java 8].
The primary routine is called `solve`. It can give the set of all
solutions for the problem in decimal:
```scala
NQueens.solve(6).foreach(println)
Vector(1, 3, 5, 0, 2, 4)
Vector(2, 5, 1, 4, 0, 3)
Vector(3, 0, 4, 1, 5, 2)
Vector(4, 2, 0, 5, 3, 1)
```
Alternatively, an application entry point, `main`, is provided:
```scala
NQueens.main(Array())
```
Gives a listing of all the solutions for 8 queens:
```
Solution #1
Q|_|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
_|_|_|_|_|_|_|Q
_|_|_|_|_|Q|_|_
_|_|Q|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|Q|_|_|_|_|_|_
_|_|_|Q|_|_|_|_
Solution #2
Q|_|_|_|_|_|_|_
_|_|_|_|_|Q|_|_
_|_|_|_|_|_|_|Q
_|_|Q|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|Q|_|_|_|_
_|Q|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
Solution #3
Q|_|_|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|Q|_|_|_|_
_|_|_|_|_|Q|_|_
_|_|_|_|_|_|_|Q
_|Q|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
_|_|Q|_|_|_|_|_
Solution #4
Q|_|_|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|_|Q|_|_|_
_|_|_|_|_|_|_|Q
_|Q|_|_|_|_|_|_
_|_|_|Q|_|_|_|_
_|_|_|_|_|Q|_|_
_|_|Q|_|_|_|_|_
[...]
Solution #89
_|_|_|_|_|_|_|Q
_|Q|_|_|_|_|_|_
_|_|_|Q|_|_|_|_
Q|_|_|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|_|Q|_|_|_
_|_|Q|_|_|_|_|_
_|_|_|_|_|Q|_|_
Solution #90
_|_|_|_|_|_|_|Q
_|Q|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
_|_|Q|_|_|_|_|_
Q|_|_|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|Q|_|_|_|_
_|_|_|_|_|Q|_|_
Solution #91
_|_|_|_|_|_|_|Q
_|_|Q|_|_|_|_|_
Q|_|_|_|_|_|_|_
_|_|_|_|_|Q|_|_
_|Q|_|_|_|_|_|_
_|_|_|_|Q|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|Q|_|_|_|_
Solution #92
_|_|_|_|_|_|_|Q
_|_|_|Q|_|_|_|_
Q|_|_|_|_|_|_|_
_|_|Q|_|_|_|_|_
_|_|_|_|_|Q|_|_
_|Q|_|_|_|_|_|_
_|_|_|_|_|_|Q|_
_|_|_|_|Q|_|_|_
Found 92 solutions
```
### Getting started
Use [sbt] to interact with the build.
```
$ sbt
```
You can run Scala from the sbt console:
```
sbt> console
scala> Main.main(Array("4"))
```
```
Solution #1
_|Q|_|_
_|_|_|Q
Q|_|_|_
_|_|Q|_
Solution #2
_|_|Q|_
Q|_|_|_
_|_|_|Q
_|Q|_|_
Found 2 solutions
```
Alternatively, you can interact with program as if it was built as a
command-line application but from sbt:
```
sbt> run 6
[info] Running Main 6
Solution #1
_|Q|_|_|_|_
_|_|_|Q|_|_
_|_|_|_|_|Q
Q|_|_|_|_|_
_|_|Q|_|_|_
_|_|_|_|Q|_
Solution #2
_|_|Q|_|_|_
_|_|_|_|_|Q
_|Q|_|_|_|_
_|_|_|_|Q|_
Q|_|_|_|_|_
_|_|_|Q|_|_
Solution #3
_|_|_|Q|_|_
Q|_|_|_|_|_
_|_|_|_|Q|_
_|Q|_|_|_|_
_|_|_|_|_|Q
_|_|Q|_|_|_
Solution #4
_|_|_|_|Q|_
_|_|Q|_|_|_
Q|_|_|_|_|_
_|_|_|_|_|Q
_|_|_|Q|_|_
_|Q|_|_|_|_
Found 4 solutions
[success] Total time: 8 s, completed Mar 4, 2019 9:30:06 AM
```
### Caveats
Passing the empty string as an argument:
```
scala> Main.main(Array(""))
java.lang.NumberFormatException: For input string: ""
```
Passing an argument that is something other than an Integer:
```
scala> Main.main(Array("f"))
java.lang.NumberFormatException: For input string: "f"
```
Passing an argument that isn't a valid Integer:
```
scala> Int.MaxValue
res1: Int = 2147483647
scala> Main.main(Array("2147483648"))
java.lang.NumberFormatException: For input string: "2147483648"
```
### References
1.
2.
[Java 8]: http://docs.oracle.com/javase/8/docs/api/
[sbt]: http://scala-sbt.org
[Scala]: http://scala-lang.org