F# で Project Euler Problem 7
素数を小さい方から6つ並べると 2, 3, 5, 7, 11, 13 であり, 6番目の素数は 13 である.
10 001 番目の素数を求めよ.
What is the 10 001st prime number?
Scala版をそのまま移植
> exception WhileBreak of unit;;
exception WhileBreak of unit
> let mutable prime_list = [2];;
val mutable prime_list : int list = [2]
> let mutable cnt = 1;;
val mutable cnt : int = 1
> let mutable num = 3;;
val mutable num : int = 3
>
- while (cnt < 10001) do
- let num_sqrt = sqrt (float num)
- let mutable fPrime = true
- try
- prime_list
- |> List.iter (fun p ->
- if ((float p) > num_sqrt) then
- raise (WhileBreak ())
- elif (num % p = 0) then
- fPrime <- false
- raise (WhileBreak ())
- )
- with _ -> ()
-
- if fPrime then
- prime_list <- List.append prime_list [num]
- cnt <- cnt + 1
- num <- num + 2
- ;;
|> List.iter (fun p ->
----------------------^
stdin(11,23): error FS0407: The mutable variable 'fPrime' is used in an invalid way. Mutable variables cannot be captured by closures. Consider eliminating this use of mutation or using a heap-allocated mutable reference cell via 'ref' and '!'.クロージャになっちゃってるのか？
> exception WhileBreak of unit;; exception WhileBreak of unit > let mutable prime_list = [2];; val mutable prime_list : int list = [2] > let mutable cnt = 1;; val mutable cnt : int = 1 > let mutable num = 3;; val mutable num : int = 3 > let mutable fPrime = true;; val mutable fPrime : bool = true > - while (cnt < 10001) do - let num_sqrt = sqrt (float num) - fPrime <- true - try - prime_list - |> List.iter (fun p -> - if ((float p) > num_sqrt) then - raise (WhileBreak ()) - elif (num % p = 0) then - fPrime <- false - raise (WhileBreak ()) - ) - with _ -> () - - if fPrime then - prime_list <- List.append prime_list [num] - cnt <- cnt + 1 - num <- num + 2 - ;; val it : unit = () > prime_list.[prime_list.Length-1];; val it : int = 104743 > ;;
Scala版 より高速！
