# SPOJ 24. Small factorials (FCTRL2) with F#

## Problem Definition

You are asked to calculate factorials of some small positive integers.

### Input

An integer t, 1<=t<=100, denoting the number of testcases, followed by t lines, each containing a single integer n, 1<=n<=100.

### Output

For each integer n given at input, display a line with the value of n!

More details about the problem is available here.

## Solution

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 open System open System.Numerics let init() = Array.init 158 (fun x -> if x = 0 then 1 else 0) let minLength (a:int array) : int = let rec m' (a:int array) i = match a.[i-1] with | 0 -> m' a (i-1) | _ -> i in m' a a.Length let toString' (a:int array) = let s = System.Text.StringBuilder() let mLength = minLength a for i=(mLength-1) downto 0 do s.Append(a.[i])|>ignore s.ToString() let (^*) multiplier (multiplicand:int array)= let rec multiplyOPT (a:int array) b i acc length= let l = Math.Min(length,a.Length) if i< l then let r = a.[i] * b + acc a.[i] <- r%10 multiplyOPT a b (i+1) (r/10) length else a in multiplyOPT multiplicand multiplier 0 0 (multiplicand |>minLength |> (+) 2) let factorial n = let rec fac n r = match n with | 0 -> toString' r | _ -> fac (n-1) (n^*r) fac n (init()) let intFactorial (i : uint64) = let rec f (i:uint64) (acc:uint64) = match i with | 0UL -> acc | i -> f (i-1UL) (acc*i) in f i 1UL let computeFactorial (n:int) = if n > 20 then factorial n else (intFactorial (n |> uint64)).ToString(); let solveSpoj24() = let rec solveLines currentLine maxLines = if currentLine < maxLines then System.Console.ReadLine() |> int |> computeFactorial |> printfn "%s" solveLines (currentLine+1) maxLines in match Console.ReadLine() |> Int32.TryParse with | (true, i) when i > 0 -> solveLines 0 i | _ -> () solveSpoj24()
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