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  1. Prepare
  2. Functional Programming
  3. Introduction
  4. Functions or Not?
  5. Discussions

Functions or Not?

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  • Rhaseven7h
     + 5 comments

    Might be helpful to know ...

    In case it is useful for someone, in the context of this challenge, a valid function is that which for a given input, ALWAYS gives the same output.

    VALID Function

    Given a function f() that functions as:

    f(1)=1
f(2)=2
f(3)=3
f(2)=2
f(4)=1000

    It is considered VALID, as outputs are always in a 1:1 relation with inputs, even although we don't know the exact way the relationship (function) works (i.e. we got no idea how f(4) gives 1000).

    INVALID Function

    A function g() which functions as follows:

    g(1)=1
g(2)=333
g(3)=89
g(2)=777
g(4)=1000

    The above function g, is NOT VALID, since, for input 2, we get two different results, first 333, then later we get 777.

    NOTE : It is worth noting that multiple inputs may give the same output:

    f(1)=99
f(2)=99
f(3)=99

    Would still be a valid function.

  • zylviij
     + 6 comments

    Here is a template for haskell.

    import Control.Monad

valid :: [(Int, Int)] -> Bool
valid f = -- code goes here --

main = do
    t <- fmap (read::String->Int) getLine
    forM [1..t] (\_->do
        n <- fmap (read::String->Int) getLine
        func <- forM [1..n] (\_->do fmap ((\[a, b]->(a,b)).map (read::String->Int).words) getLine :: IO (Int, Int))
        putStrLn $ if valid func then "YES" else "NO")

  • vestail
     + 3 comments

    My strange scala solution.

    object Solution {
  def main(args: Array[String]) {
    val n = io.StdIn.readInt()
    (1 to n).foreach { i =>
      val k = io.StdIn.readInt()
      val list = (1 to k).map(x => io.StdIn.readLine.split("\\s+")(0)).toList
      if (list.distinct.size == list.size) println("YES")
      else println("NO")
    }
  }
}

  • Tleilaxi
     + 4 comments

    I think there is a problem in the input of the tests case of OCaml. Just doing the simple

    let a = read_int ();;

    that should normally read the first line of the input (the number of tests cases), fail with the exception

    "int_of_string"

    meaning that the conversion was impossible. There's probably an odd character or byte in the input that' s not displayed when it's printed, because when I copy/paste the inputs of the tests cases as displayed in my browser and run them with "Test against custom input", they execute without errors.

  • GeneralGrievous
     + 3 comments

    This input is a bit tricky. My code may help F# folks.

    open System

let readList n parser =
    Seq.initInfinite (fun _ -> Console.ReadLine())
    |> Seq.take n
    |> Seq.map parser
    |> Seq.toList

let parseRelation (s: string) =
    match s.Split(' ') with
    | [|x|] -> int x, None
    | [|k; v|] -> int k, Some (int v)
    | _ -> failwith "OhGodWhy"

let readTestCase () =
    let n = int <| Console.ReadLine()

    readList n parseRelation

let isFunc relations =
    relations
    |> Map.ofList
    |> Map.toSeq
    |> Seq.length
    |> (=) (List.length relations)

let boolStr = function
    | true -> "YES"
    | false -> "NO"

[<EntryPoint>]
let main args =
    let t = int <| Console.ReadLine()

    Seq.initInfinite (fun _ -> readTestCase ())
    |> Seq.take t
    |> Seq.map isFunc
    |> Seq.map boolStr
    |> Seq.iter (printfn "%s")

    0
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