シフト暗号

# プログラム

`-- If you want to use it type something like:-- let tmp = encode 3 "Zombies ate my brains"-- crack tmp​import Data.Char​helper = zip ['a'..'z'] [0..25]​let2num::Char -> Intlet2num c = head [ b | (a,b) <- helper, a==c]num2let d = head [ a | (a,b) <- helper, b==(d `mod` length helper)]​shift num c = if isLower c == False              then c              else num2let( (let2num c) + num )​encode::Int->String->Stringencode num = map (shift num)decode num = map (shift ((length helper) - num))​lowers s = fromIntegral (length (filter isLower s ) )count c s = fromIntegral (length (filter(==c) s) )percent a b = (a/b)*100​freq::String->[Float]freq s = [percent (count a s) (lowers s) | a<-['a'..'z']]​rotate::Int->String->Stringrotate d s = (drop d s) ++ (take d s)​chisqr::[Float]->[Float]->Floatchisqr os es = sum [(a-b)^2/b | (a,b) <- zip os es]​position x xs = head [ b | (a,b) <- zip xs [0..(length xs -1)], a==x ]​freqArray s = [chisqr (freq (decode a s)) table | a <- [0..25]]​crack s = decode (position (minimum (freqArray s)) (freqArray s)) s​table::[Float]table = [8.2, 1.5, 2.8, 4.3, 12.7, 2.2, 2.0, 6.1, 7.0,         0.2, 0.8, 4.0, 2.4, 6.7, 7.5, 1.9, 0.1, 6.0,         6.3, 9.1, 2.8, 1.0, 2.4, 0.2, 2.0, 0.1]`