Question

Hmmm… its kinda challenging to find a method for reading/writing data faster enough to get ACCEPTED in this problem ( https://www.spoj.pl/problems/INTEST/ ) using F#.

My code ( http://paste.ubuntu.com/548748/ ) gets TLE…

Any ideas how to speed up data reading?

Answer 1

This version of mine passes the time limit (but is still terribly slow ~14 seconds):

open System
open System.IO

// need to change standard buffer, not to add an additional one
let stream = new StreamReader(Console.OpenStandardInput(4096))

let stdin = Seq.unfold (fun s -> if s = null then None else Some (s,stream.ReadLine())) <| stream.ReadLine()

let inline s2i (s : string) = Array.fold (fun a d -> a*10u + (uint32 d - uint32 '0') ) 0u <| s.ToCharArray()

let calc = 
    let fl = Seq.head stdin
    let [|_;ks|] = fl.Split(' ')
    let k = uint32 ks
    Seq.fold (fun a s -> if (s2i s) % k = 0u then a+1 else a) 0 <| Seq.skip 1 stdin

printf "%A" calc

Though the bottle-neck of this version is actually string -> uint32 conversion (standard uint32 cast from string is even slower) the reading itself takes around 2 sec (vs 6 sec of total time) on my sample input (~100M file) – still not a great result. Once s2i is rewritten in imperative style, the total run-time can be reduced to 10 sec on spoj:

let inline s2i (s : string) =
    let mutable a = 0u
    for i in 0..s.Length-1 do a <- a*10u + uint32 (s.Chars(i)) - uint32 '0'
    a