pairs.elm

import Html exposing (text)
import Set
import List

main =
  -- text (toString (List.sum (pairs [1, 5, 3, 4, 2] 2)))
  text (toString (List.sum (pairs [363374326, 364147530, 61825163, 1073065718, 1281246024, 
                                  1399469912, 428047635, 491595254, 879792181, 1069262793] 
                                  1)))

check i k b counter =
    let
        lower = i - k
    in
        if Set.member lower b then
            counter + 1
        else
            counter


pairs a k =
    let
        answer = 0
        b = Set.fromList a
    in
        List.map (\ i -> check i k b answer) a