$ cat p5.hs
import Debug.Trace
output lst _ _ [] = lst
output lst _ [] _ = lst
output lst n (x:xs) (y:ys)
| n==x = output (lst++[y]) (n+1) (xs) ys
| otherwise = output lst (n+1) (x:xs) ys
filt100 lst n [] = lst
filt100 lst n (x:xs)
| x==100 = filt100 (lst++[n]) (n+1) xs
| otherwise = filt100 lst (n+1) xs
calc (x:[]) = x
calc (x:y:z:xs)
| y=="+" = calc $ (show (read x+read z)):xs
| y=="-" = calc $ (show (read x-read z)):xs
listup :: Int -> [String]
listup n
| n<9 = map ((show n ++ " + ") ++) (listup (n+1)) ++
map ((show n ++ " - ") ++) (listup (n+1)) ++
map (show n ++) (listup (n+1))
| otherwise = [show n]
main = do
let lists = listup 1
let arr = filt100 [] 0 $ map read $ map calc $ map words lists
mapM_ putStrLn $ map (foldr1 (++)) $ map words $ output [] 0 arr lists
$ time ./p5
1+2+3-4+5+6+78+9
1+2+34-5+67-8+9
1+23-4+5+6+78-9
1+23-4+56+7+8+9
12+3+4+5-6-7+89
12+3-4+5+67+8+9
12-3-4+5-6+7+89
123+4-5+67-89
123+45-67+8-9
123-4-5-6-7+8-9
123-45-67+89
real 0m0.296s
user 0m0.284s
sys 0m0.009s
- letで束縛したリストを複数回使っているあたりが手続き的だし、最適化されていないところ
- 以下記事を見るとどうやら自分がguardをうまく使いこなせていない、ということが分かる
qiita.com
訂正
$ cat p5_2.hs
import Debug.Trace
filtfunc str = case read . calc $ words str of
100 -> True
_ -> False
calc (x:[]) = x
calc (x:y:z:xs) = case y of
"+" -> calc $ (show (read x+read z)):xs
"-" -> calc $ (show (read x-read z)):xs
listup :: Int -> [String]
listup n
| n<9 = map ((show n ++ " + ") ++) (listup (n+1)) ++
map ((show n ++ " - ") ++) (listup (n+1)) ++
map (show n ++) (listup (n+1))
| otherwise = [show n]
main = do
mapM_ putStrLn $ map (foldr1 (++)) $ map words $ filter filtfunc $ listup 1
$ time ./p5_2
1+2+3-4+5+6+78+9
1+2+34-5+67-8+9
1+23-4+5+6+78-9
1+23-4+56+7+8+9
12+3+4+5-6-7+89
12+3-4+5+67+8+9
12-3-4+5-6+7+89
123+4-5+67-89
123+45-67+8-9
123-4-5-6-7+8-9
123-45-67+89
real 0m0.305s
user 0m0.293s
sys 0m0.008s
