purescript-nqueens

PureScript package to calculate the N-Queens problem. Currently only supports the naive backtracking implementation.

🔎 Please check out my post about this: Solving N-Queens with PureScript!

Official Pursuit documentation: https://pursuit.purescript.org/packages/purescript-nqueens

Project Structure

The library itself is in src, the live demo is hosted on GitHub pages at https://jrrom.github.io/purescript-nqueens, the code for which is in demo.

Note: I would like to credit Classless.css for the stylesheet.

Reason for development

I created this package to learn about functional backtracking algorithms for an assignment. It allows users an easy way to calculate N-Queens. It is intended for general use in programs, given that the value of n is small. It works great in the REPL thanks to the custom implementation of the Show instance.

Install instructions

spago install nqueens

Usage

purescript-nqueens exports nQueensNaive, boardSize, boardQueens and the Board type. A Board represents { size :: Int, queens :: List Position } where size is the n in n x n and queens is a List of Position :: { row :: Int, col :: Int }.

module Main where

import Prelude

import Data.Foldable (traverse_)
import Data.List (length, List(..), (:))
import Data.NQueens (nQueensNaive, boardSize, boardQueens)
import Effect (Effect)
import Effect.Class.Console (logShow)

main :: Effect Unit
main = do
  let solutions = nQueensNaive 4
  traverse_ (logShow <<< boardQueens) solutions
  case solutions of
    x:_ -> logShow (boardSize x)
    Nil -> pure unit
  logShow solutions
  logShow ("Number of solutions: " <> show (length solutions))

Result :-

({ col: 2, row: 3 } : { col: 0, row: 2 } : { col: 3, row: 1 } : { col: 1, row: 0 } : Nil)
({ col: 1, row: 3 } : { col: 3, row: 2 } : { col: 0, row: 1 } : { col: 2, row: 0 } : Nil)
4
(
 _  Q  _  _
 _  _  _  Q
 Q  _  _  _
 _  _  Q  _
 :
 _  _  Q  _
 Q  _  _  _
 _  _  _  Q
 _  Q  _  _
 : Nil)
"Number of solutions: 2"

Disclaimer

I made this for a personal assignment of mine. Time complexity is exponential for the naive implementation so performance is poor for any n > 10.

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.