program ex_7_18_v
use Environment

implicit none
character(*), parameter :: input_file = "../data/input.txt", output_file = "output.txt"
integer :: In = 0, Out = 0, N = 0, i = 0, j=0, l, N_max, m, k
real(R_) :: max
real(R_), allocatable :: A(:, :), B(:)
integer, allocatable :: Indexes(:, :), Ind_max(:, :)
logical, allocatable :: Mask(:)

!READ AN NxN ARRAY
open (file=input_file, newunit=In)
read (In, *) N
allocate (A(N, N))
allocate (B(2*N))
read (In, *) (A(i, :), i = 1, N)
close (In)

allocate (Indexes(2*N, 2)) !AN N*N MATRIX CONTAINS M*N ELEMENTS. THIS ARRAY WILL CONTAIN INDICES COLUMNWISE.
allocate (Mask(N), source=.false.)

!Indexes(:, 1) = [((i, i = 1, N), j = 1, N)]
!Indexes(:, 2) = [((j, i = 1, N), j = 1, N)]

i=1
j=1
do m=1, N
B(i) = abs(A(i, i))
Indexes(i, 1) = i
Indexes(i, 2) = j
write (Out, *) Indexes(i, :)
i=i+1
j=j+1
end do

i=N
l=N+1
j=1
do k=1, N
B(l) = abs(A(i, j))
Indexes(i, 1) = i
Indexes(i, 2) = j
write (Out, *) Indexes (i, :)
i=i-1
l=l+1
j=j+1
end do

write (Out, *) Indexes(:, :)

max=maxval(B)
mask = [B == max]
N_max = count(Mask)
write (Out, *) N_max

allocate (ind_max(N_max, 2))
Ind_max(:, 1) = Pack(Indexes(:, 1), Mask)
Ind_max(:, 2) = Pack(Indexes(:, 2), Mask)

open (file=output_file, encoding=E_, newunit=Out)
write (Out, *) (A(i, :), i = 1, N)
write (Out, *) "------------------------"
write (Out, *) B
write (Out, *) "MAX = ", max
write (Out, *) (Ind_max(i, :), i = 1, UBound(Ind_max, 1))
close (Out)

end program ex_7_18_v