e59.scala

import scala.io.Source

val code = Source.fromURL("http://projecteuler.net/project/cipher1.txt").mkString.trim.split(",").map(_.toInt.toChar).toList

def decode(pass: List[Char], code: List[Char]): List[Char] =
  code.zipWithIndex.map( p => p._1 ^ pass(p._2 % pass.length) toChar )

val frequentlyWord = "the".r
def isGraphicChar(c: Char): Boolean = return if (c < ' ' || '~' < c) false else true
val passes = for (a <- 'a' to 'z'; b <- 'a' to 'z'; c <- 'a' to 'z') yield List(a, b, c)

val correctPass = passes.maxBy { pass =>
  val decoded = decode(pass, code)
  if (decoded.forall(isGraphicChar)) frequentlyWord.findAllIn(decoded.mkString).length else -1
}

println(correctPass) // => List(g, o, d)
println(decode(correctPass, code).mkString) // => (The Gospel of ...

val answer = decode(correctPass, code).map(_.toInt).sum
println(answer) // => 107359