gistfile1.hs

{-# LANGUAGE BangPatterns #-}
import Control.Applicative
import Prelude hiding (minimum, sum)
import Data.List (permutations)
import Control.Monad.ST
import Data.Bifunctor (second)
import Data.Vector.Unboxed (Vector)
import qualified Data.Vector.Unboxed as U
import Data.Vector.Unboxed.Mutable (STVector)
import qualified Data.Vector.Unboxed.Mutable as UM

import Data.Foldable

data Exp = IfGt !Int !Int !Block !Block -- if a[i] > a[j] then blk1 else blk2
         | Swap !Int !Int  -- a[i] <-> a[j]  (i,j < 8)
         | Copy !Int !Int  -- a[i] <- a[j]  (i > 7)
         deriving Show

type Block = [Exp]

evalBlock :: STVector s Int -> Block -> ST s Int
evalBlock a es = go es 0
  where
    go [] !n = return n
    go (e:es) !n = do
      !n2 <- eval e
      go es (n + n2)

    eval (IfGt i j !b1 !b2) = do
      ai <- a `UM.unsafeRead` i
      aj <- a `UM.unsafeRead` j
      if ai > aj then go b1 1 else go b2 1
    eval (Swap i j) = do
      ai <- a `UM.unsafeRead` i
      aj <- a `UM.unsafeRead` j
      UM.unsafeWrite a i aj
      UM.unsafeWrite a j ai
      return 1
    eval (Copy i j) = do
      aj <- a `UM.unsafeRead` j
      UM.unsafeWrite a i aj
      return 1



numSteps :: Block -> Vector Int -> Int
numSteps blk ua = runST $ do
  a  <- U.thaw ua
  n  <- evalBlock a blk
  r1 <- a `UM.unsafeRead` 1
  r6 <- a `UM.unsafeRead` 6
  return $ if r1 == 2 && r6 == 7 then n else 25000

inputs :: [Vector Int]
inputs = let ps = permutations [1..8]
             zs = [0,0,0,0]
         in [ U.fromListN 12 (p ++ zs) | p <- ps]

calcScore :: Block -> Int
calcScore blk = sum $ map (numSteps blk) inputs

cmp_swap i j = IfGt i j [Swap i j] []

mksornet cmp =
         [cmp 0 1, cmp 2 3, cmp 4 5, cmp 6 7,
          cmp 0 2, cmp 1 3, cmp 4 6, cmp 5 7,
          cmp 1 2, cmp 5 6, cmp 0 4, cmp 3 7,
          cmp 1 5, cmp 2 6,
          cmp 1 4, cmp 3 6]

sornet :: Block
sornet = mksornet cmp_swap

main = print . minimum . map calcScore $ [Copy 10 (x `mod` 10) : sornet | x <- [1..40]]