Straddling checkerboard: Difference between revisions

=={{header|Haskell}}==

<lang haskell>import Data.Char

import Data.Map

charToInt :: Char -> Int

charToInt c = ord c - ord '0'

-- Given a string, decode a single character from the string.

-- Return the decoded char and the remaining undecoded string.

decodeChar :: String -> (Char,String)

decodeChar ('7':'9':r:rs) = (r,rs)

decodeChar ('7':r:rs) = ("PQUVWXYZ. " !! charToInt r, rs)

decodeChar ('3':r:rs) = ("ABCDFGIJKN" !! charToInt r, rs)

decodeChar (r:rs) = ("HOL MES RT" !! charToInt r, rs)

-- Decode an entire string.

decode :: String -> String

decode [] = []

decode st = let (c, s) = decodeChar st in c:decode s

-- Given a string, decode a single character from the string.

-- Return the decoded char and the part of the encoded string

-- used to encode that character.

revEnc :: String -> (Char, String)

revEnc enc = let (dec, rm) = decodeChar enc in (dec, take (length enc - length rm) enc)

ds :: String

ds = ['0'..'9']

-- Decode all 1000 possible encodings of three digits and

-- use results to construct map used to encode.

encodeMap :: Map Char String

encodeMap = fromList [ revEnc [d2,d1,d0] | d2 <- ds, d1 <- ds, d0 <- ds ]

-- Encode a single char using encoding map.

encodeChar :: Char -> String

encodeChar c = findWithDefault "" c encodeMap

-- Encode an entire string.

encode :: String -> String

encode st = concatMap encodeChar $ fmap toUpper st

-- Test by encoding, decoding, printing results.

main = let orig = "One night-it was on the twentieth of March, 1888-I was returning"

enc = encode orig

dec = decode enc

in mapM_ putStrLn [ "Original: " ++ orig

, "Encoded: " ++ enc

, "Decoded: " ++ dec ]</lang>

{{out}}

<pre style="font-size:80%">Original: One night-it was on the twentieth of March, 1888-I was returning

Encoded: 139539363509369743061399059745399365901344308320791798798798367430685972839363935

Decoded: ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING

</pre>