multiS.hs

gistfile1.txt

import Data.Ord
import Data.Char

padLeft xs x k = replicate k x ++ xs

padRight xs x k = xs ++ replicate k x

addHelper xs = fixer . foldr go (0, []) . zip xs
    where go (x, y) (carry, zs) | t >= 10 = (1, chr (t - 10 + ord '0'): zs)
                                | t  < 10 = (0, chr (t + ord '0'): zs)
            where t = ord x - ord '0' + ord y - ord '0' + carry
          fixer (0, xs) = xs
          fixer (1, xs) = '1' : xs

addString xs [] = xs
addString [] ys = ys
addString xs ys
    | length xs < length ys = addString ys xs
    | length xs >= length ys = addHelper xs (padLeft ys '0' (length xs - length ys))

multi1 xs k
    | k == 0 = []
    | k == 1 = xs
    | k == 2 = addString xs xs
    | k == 3 = addString xs (multi1 xs 2)
    | k == 4 = addString (multi1 xs 2) (multi1 xs 2)
    | k == 5 = addString (multi1 xs 2) (multi1 xs 3)
    | k == 6 = addString (multi1 xs 3) (multi1 xs 3)
    | k == 7 = addString (multi1 xs 3) (multi1 xs 4)
    | k == 8 = addString (multi1 xs 4) (multi1 xs 4)
    | k == 9 = addString (multi1 xs 4) (multi1 xs 5)

multiString xs [] = []
multiString [] ys = ys
multiString xs ys
    | length xs < length ys = multiString ys xs
    | length xs >= length ys = snd $ foldr go (0, []) ys
    where go y (k, zs) = (1 + k, addString zs (padRight (multi1 xs (ord y - ord '0')) '0' k))