Let's play Haskell! - #7 - simple json & recycled numbers solution

MyJson.hs

module MyJson where

import Data.List

data JValue = JString String
            | JBool Bool
            | JNumber Double
            | JNull
            | JList [JValue]
            | JObject [(String, JValue)]
          
instance Show JValue where
         show = renderJValue

renderJValue :: JValue -> String
renderJValue JNull = "null"
renderJValue (JBool True) = "true"
renderJValue (JBool False) = "false"
renderJValue (JString s) = show s
renderJValue (JNumber n) = show n
renderJValue (JList vs) = "[" ++ listItems ++ "]"
             where listItems = intercalate ", " $ map renderJValue vs
renderJValue (JObject pairs) = "{" ++ objectItems ++ "}"
             where objectItems = intercalate ", " $ map pairToString pairs
                   pairToString (key, jsonValue) = show key ++ ": " ++ renderJValue jsonValue

recycled-sample.in

4
1 9
10 40
100 500
1111 2222

recycled-sample.in.out

0
3
156
287

recycled.hs

rotate :: String -> [String]
rotate l = rotate_recursive l []
 
rotate_recursive :: String -> String -> [String]
rotate_recursive [] list = []
rotate_recursive list1 list2 =
	let (h1:t1) = list1
	in [list1 ++ list2] ++ rotate_recursive t1 (list2 ++ [h1])
 
-- http://code.google.com/codejam/contest/1460488/dashboard#s=p2
 
is_recycled :: String -> String -> Bool
is_recycled l1 l2 = length [ x | x <- rotate l1, x /= l1, x == l2] >= 1
 
recycled_numbers :: Int -> Int -> Int
recycled_numbers from to = length [ (x,y) |
	x <- [from..to], y <- [from..to], x < y, is_recycled (show x) (show y) ]

main :: IO ()
main = interact solve

solve :: String -> String
solve cases = unlines $ map solveCase $ drop 1 $ lines cases

solveCase :: String -> String
solveCase s = show $ recycled_numbers (read from) (read to)
          where [from, to] = words s