gistfile1.hs

rInt :: String -> Int
rInt = read

count :: String -> Int
count []       = 1
count (a:[])   = 1
count (a:b:c)  = count (b:c) + twice
  where
    twice = if isValid (a:b:[]) then count c else 0
    isValid s = (rInt s) < 27

count "12325" -> 6
count "11134" -> 5
count "12345" -> 3
count "1123"   -> 5