PKU 2718 Smallest Difference

gistfile1.fs

let size = System.Console.ReadLine() |> int
let input = [|
  for i = 0 to size - 1 do
    yield System.Console.ReadLine().Split([|' '|]) |> Array.map int
|]

let rec permutations list taken = 
  seq { if Set.count taken = List.length list then yield [] else
        for l in list do
          if not (Set.contains l taken) then 
            for perm in permutations list (Set.add l taken)  do
              yield l::perm }

let xs = List.ofArray input.[0]

let toInt (xs : int list) = 
  let mutable total = 0
  for x in List.rev (List.map (fun x -> x) xs) do
    total <- 10*total + x
  total

seq {
  for x in permutations xs Set.empty do
    let l = Seq.length x/2
    if Seq.head x <> 0 then
     if Seq.head (Seq.skip (l-1) x) <> 0 then
      yield (Seq.take (l-1) x, Seq.skip (l-1) x)
     if Seq.head (Seq.skip l x) <> 0 then
      yield (Seq.take (l) x, Seq.skip (l) x)
     if Seq.head (Seq.skip (l+1) x) <> 0 then
      yield (Seq.take (l+1) x, Seq.skip (l+1) x)
}
|> Seq.map (fun (a, b) -> System.Math.Abs(toInt (List.ofSeq a) - toInt (List.ofSeq b)))
|> Seq.min
|> printfn "%A"