gistfile1.txt

*Main> maxPointsOnLine [(1,1), (3,2), (5,3), (4,1), (2,3), (1,4)]
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maxPointsOnLine.hs

import Data.List
import Data.Ord

type Point = (Float, Float)
data Line = Line { yInt :: Float, slope :: Float } deriving (Eq, Show, Ord)

lineFromPoints :: Point -> Point -> Line
lineFromPoints p1 p2 = Line { slope = s, yInt = snd p1 - s * fst p1 }
  where x = fst p2 - fst p1
        y = snd p2 - snd p1
        s = y / x

maxPointsOnLine :: [Point] -> Int
maxPointsOnLine ps = 1 + n
  where n = maximum . concat $                          -- find max freq
              [map length . group . sort $              -- get freq of lines
              [lineFromPoints x y | y <- ys ]           -- find lines b/w
                                  | (x:ys) <- tails ps] -- all unique pairs