Brute force solver 1

Solver1.hs

module Solver1 where

import Data.Ord (comparing)
import Data.Foldable (minimumBy)

maxVal :: [(Int, Int)] -> Int
maxVal l = max (maximum l1) (maximum l2)
  where
    (l1, l2) = unzip l

best :: [[(Int, Int)]] -> [(Int, Int)]
best = minimumBy $ comparing maxVal

gen :: Int -> Int -> (Int, Int) -> (Int, Int) -> [(Int, Int)]
gen 0 _ _           __      = []
gen n m p@(ap, bp) (an, bn) = best $ assign <$> els
  where
    els = if n == 1
      then [(a, b) | a <- [1..m], b <- [1..m], a /= b, a /= an, b /= bn, a /= bn, b /= an, a /= ap, b /= bp, a /= bp, b /= ap]
      else [(a, b) | a <- [1..m], b <- [1..m], a /= b, a /= an, b /= bn, a /= bn, b /= an]
    assign e = e : gen (n - 1) m p e

solve :: Int -> Int -> [(Int, Int)]
solve n m = best $ assign <$> els
  where
    els = [(a, b) | a <- [1..m], b <- [1..m], a /= b]
    assign e = e : gen (n - 1) m e e

main :: IO ()
main = do
  putStrLn $ "result for 4: " ++ show (solve 4 6)
  putStrLn $ "result for 5: " ++ show (solve 5 6)