advent2017-day15.fs

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Problem A
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

let generate factor seed =
    seed
    |> Seq.unfold (
        fun previous ->
            let result = (previous * factor) % 2147483647L
            Some (result,result))
            
let generatorA = generate 16807L
let generatorB = generate 48271L

let result comparisonsCount filterA filterB =
    Seq.zip (generatorA 116L |> Seq.filter filterA) (generatorB 299L |> Seq.filter filterB)
    |> Seq.take comparisonsCount
    |> Seq.fold
        (fun matches (a,b) ->
            let aTrimmed = a &&& 0xFFFFL
            let bTrimmed = b &&& 0xFFFFL
            matches + (if aTrimmed = bTrimmed then 1 else 0))
        0 // seed
        
let acceptAll _ = true
(result 40000000 acceptAll acceptAll).Dump("Number of matches")


// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Problem B
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

let divisibleBy factor value = (value % factor) = 0L
(result 5000000 (divisibleBy 4L) (divisibleBy 8L)).Dump("Number of matches with filtered streams")