Problem 81

http://projecteuler.net/index.php?section=problems&id=81

ものすごくそのままなDP

import Data.Array.IArray
import Control.Monad
root ::Array (Int,Int) Integer->Array (Int,Int) Integer
root cost = r
where r = listArray b 
b = bounds cost
c (i,j) = cost!(i,j) + f [r!ix|ix<-[(i+1,j),(i,j+1)],inRange b ix]
f [] = 
f [a] = a
f [a,b] = min a b
mkArray ::String->Array (Int,Int) Integer
mkArray ws= listArray ((1,1),(m,m)) ws'
where ws'=concat.map (read.g).lines$ws
m = floor.sqrt.fromIntegral.length$ws'
g x = "["++x++"]"
main = liftM((!(1,1)).root.mkArray).readFile$"matrix.txt"