Euler18.hs

module Euler18 where
import Data.Map hiding (map)
import Data.List (scanr)

lst :: [[Integer]]
lst =   [
	  [75]
	, [95,64]
	, [17,47,82]
	, [18,35,87,10]
	, [20,04,82,47,65]
	, [19,01,23,75,03,34]
	, [88,02,77,73,07,63,67]
	, [99,65,04,28,06,16,70,92]
	, [41,41,26,56,83,40,80,70,33]
	, [41,48,72,33,47,32,37,16,94,29]
	, [53,71,44,65,25,43,91,52,97,51,14]
	, [70,11,33,28,77,73,17,78,39,68,17,57]
	, [91,71,52,38,17,14,91,43,58,50,27,29,48]
	, [63,66,04,68,89,53,67,30,73,16,69,87,40,31]
	, [04,62,98,27,23,09,70,98,73,93,38,53,60,04,23]
        ]



table = fromList $ lst2
       where
        lst2 = concat $ map (\x-> zipWith (\a b ->((fromIntegral (length  x) , a),b)) [1..] x) lst


euler18 = foldr1 max (f 1 1 0)
    where
      bound = 15
      f n m s
          |  n == bound = [sum']
          |  otherwise  = (f (n+1) m sum') 
                          ++ (f (n+1) (m+1) sum')
                              where                
                                sum'  = table!(n,m) + s

そんな答えで大丈夫か？

NG コード

g xs | (length xs) >= n = take n xs : g (drop n xs)
| otherwise = [xs]
where n = 15

z n m
| n == bound = [(n,m)]
| otherwise = ((n,m):(z (n+1) m)) ++ ((n,m):(z (n+1) (m+1)))
where
bound = 15

動的計画法使うかと思ったけど、全然使わなかった

これって結局二分木の探索みたいな感じだた

このコードはエレガントで素晴らしい
http://tsumuji.cocolog-nifty.com/tsumuji/2010/04/project-euler-.html