[ch-086/jeongoon] ch-1.hs added

1 files changed, 41 insertions, 0 deletions

diff --git a/challenge-086/jeongoon/haskell/ch-1.hs b/challenge-086/jeongoon/haskell/ch-1.hs
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+++ b/challenge-086/jeongoon/haskell/ch-1.hs
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+import System.Environment
+import System.Exit
+import Data.Char (isNumber)
+import Data.Maybe (isNothing, catMaybes)
+import Data.List (sort)
+
+{- tested with:
+runhaskell ch-1.hs  1 3 2 -1 -2 -3 6 7 9 1
+1 as 3 -2 = 1
+-}
+
+usageMessage = "Usage: runhaskell ch-1.hs "
+               ++ "<target diff(positive integer)> <integer> ..."
+
+pairDifference _      [] = Nothing
+pairDifference target ls = pairdiff target (head sorted) (tail sorted) 1
+  where
+    sorted = sort ls
+    pairdiff _ _ [] _ = Nothing
+    pairdiff t f rst@(r:_) i = -- t: target, f: first, i: index
+      if i >= (length rst) then Nothing
+      else case ((rst !! i) - f) `compare` t of
+             LT -> pairdiff t f rst (succ i)
+             GT -> pairdiff t r rst 1
+             EQ -> Just (f, (rst !! i))
+
+main = do
+  ints <- (catMaybes.map (\nStr ->
+                            if (all isNumber nStr) then Just(read nStr :: Int)
+                            else Nothing )) `fmap` getArgs;
+
+  let d = (head ints) in
+
+    if (length ints) < 2
+    then die usageMessage
+    else if d < 0
+         then die usageMessage
+         else case pairDifference d (tail ints) of
+                Nothing    -> putStrLn "0"
+                Just (a,b) -> putStrLn $ "1 as " ++ (show b) ++ " - "
+                  ++ (show a) ++ " = " ++ (show d)