September 2017 Update

Task/Rep-string/Haskell/rep-string-2.hs

@@ -0,0 +1,48 @@
+import Data.List (inits, intercalate, transpose)
+
+-- REP-CYCLES -----------------------------------------------------------------
+repCycles :: String -> [String]
+repCycles cs =
+  let n = length cs
+  in filter ((cs ==) . take n . cycle) (tail $ inits (take (quot n 2) cs))
+
+cycleReport :: String -> [String]
+cycleReport xs =
+  let reps = repCycles xs
+  in [ xs
+     , if not (null reps)
+         then last reps
+         else "(n/a)"
+     ]
+
+-- TEST -----------------------------------------------------------------------
+main :: IO ()
+main = do
+  putStrLn "Longest cycles:\n"
+  putStrLn $
+    unlines $
+    table "  -> " $
+    cycleReport <$>
+    [ "1001110011"
+    , "1110111011"
+    , "0010010010"
+    , "1010101010"
+    , "1111111111"
+    , "0100101101"
+    , "0100100"
+    , "101"
+    , "11"
+    , "00"
+    , "1"
+    ]
+
+-- GENERIC --------------------------------------------------------------------
+table :: String -> [[String]] -> [String]
+table delim rows =
+  intercalate delim <$>
+  transpose
+    ((\col ->
+         let width = (length $ maximum col)
+             justifyLeft n c s = take n (s ++ replicate n c)
+         in justifyLeft width ' ' <$> col) <$>
+     transpose rows)