Task: Count in factors








VB: Function CountFactors(n)
	If n = 1 Then
		CountFactors = 1
	Else
		arrP = Split(ListPrimes(n)," ")
		Set arrList = CreateObject("System.Collections.ArrayList")
		divnum = n
		Do Until divnum = 1
			
			For i = 0 To UBound(arrP)-1
				If divnum = 1 Then
					Exit For
				ElseIf divnum Mod arrP(i) = 0 Then
					divnum = divnum/arrP(i)
					arrList.Add arrP(i)
				End If
			Next
		Loop
		arrList.Sort
		For i = 0 To arrList.Count - 1
			If i = arrList.Count - 1 Then
				CountFactors = CountFactors & arrList(i)
			Else
				CountFactors = CountFactors & arrList(i) & " * "
			End If
		Next
	End If
End Function
 
Function IsPrime(n)
	If n = 2 Then
		IsPrime = True
	ElseIf n <= 1 Or n Mod 2 = 0 Then
		IsPrime = False
	Else
		IsPrime = True
		For i = 3 To Int(Sqr(n)) Step 2
			If n Mod i = 0 Then
				IsPrime = False
				Exit For
			End If
		Next
	End If
End Function
 
Function ListPrimes(n)
	ListPrimes = ""
	For i = 1 To n
		If IsPrime(i) Then
			ListPrimes = ListPrimes & i & " "
		End If
	Next
End Function


WScript.StdOut.Write "2 = " & CountFactors(2)
WScript.StdOut.WriteLine
WScript.StdOut.Write "2144 = " & CountFactors(2144)
WScript.StdOut.WriteLine



Fortran: 













































module prime_mod

  
  integer, dimension(:), allocatable :: sieve_table
  private :: PrimeQ

contains

  
  subroutine sieve(n) 
    integer, intent(in) :: n
    integer :: status, i, j
    if ((n .lt. 1) .or. allocated(sieve_table)) deallocate(sieve_table)
    if (n .lt. 1) return
    allocate(sieve_table(n), stat=status)
    if (status .ne. 0) stop 'cannot allocate space'
    sieve_table(1) = 1
    do i=2,int(sqrt(real(n)))+1
       if (sieve_table(i) .eq. 0) then
          do j = i*i, n, i
             sieve_table(j) = i
          end do
       end if
    end do
  end subroutine sieve

  subroutine check_sieve(n)
    integer, intent(in) :: n
    if (.not. (allocated(sieve_table) .and. ((1 .le. n) .and. (n .le. size(sieve_table))))) stop 'Call sieve first'
  end subroutine check_sieve

  logical function isPrime(p)
    integer, intent(in) :: p
    call check_sieve(p)
    isPrime = PrimeQ(p)
  end function isPrime

  logical function isComposite(p)
    integer, intent(in) :: p
    isComposite = .not. isPrime(p)
  end function isComposite

  logical function PrimeQ(p)
    integer, intent(in) :: p
    PrimeQ = sieve_table(p) .eq. 0
  end function PrimeQ

  subroutine prime_factors(p, rv, n)
    integer, intent(in) :: p 
    integer, dimension(:), intent(out) :: rv 
    integer, intent(out) :: n 
    integer :: i, m
    call check_sieve(p)
    m = p
    i = 1
    if (p .ne. 1) then
       do while ((.not. PrimeQ(m)) .and. (i .lt. size(rv)))
          rv(i) = sieve_table(m)
          m = m/rv(i)
          i = i+1
       end do
    end if
    if (i .le. size(rv)) rv(i) = m
    n = i
  end subroutine prime_factors

end module prime_mod

program count_in_factors
  use prime_mod
  integer :: i, n
  integer, dimension(8) :: factors
  call sieve(40)                
  do i=1,40
     factors = 0
     call prime_factors(i, factors, n)
     write(6,*)'assert',i,'= */',factors(:n)
  end do
  call sieve(0)                 
end program count_in_factors