AmicablePairsReadSumsFromDisk.f95

program amicable_pairs_sumsfromfile
	! Juhani Kaukoranta 24.4.2020
    ! Lukee kokonaislukujen summataulukon levyltä
    ! ja laskee sen avulla ystäväparit
    implicit none
    integer, dimension(40000000) :: divsum
    integer :: m, n, i, j, maxn, nro
    real :: t0, t1
    n = 40000000
    m = n / 4
    call cpu_time(t0)
    open (10, file ='summat.dat')
    do i = 1, n
        read (10,*) divsum(i)
    end do
    close(10)
    call cpu_time(t1)
    write (*,*) "summataulukon lukeminen ",t1-t0," sekuntia"
    maxn = maxval(divsum)
    write (*,*) "n = ",n
    write (*,*) "m = ",m
    write (*,*) "maksimisumma = ",maxn
    write (*,*) "Ystäväparit, jotka ovat pienempiä kuin ",m
    call cpu_time(t0)
    nro = 0
    do i = 1, m
        j = divsum(i)
        if (i < j .and. i == divsum(j)) then
            nro = nro+1
            write (*,*) nro,": ", i, " ",divsum(i)
        end if
    end do
    call cpu_time(t1)
    write (*,*) "amicable pairs laskemisaika ",t1-t0," sekuntia"

end program amicable_pairs_sumsfromfile