permutations with repetition algorithm?

Question

I\'m trying to write a code in Fortran that generates that given the following input 1,2,3 generates the permutations with repetition:

111 112 113 121 122 123 . . .<

Answer 1

Here is one solution:

module perm_mod
contains
  subroutine print_permutations(A)
    implicit none
    integer,intent(in)    :: A(:)
    integer               :: i, j, l, remainder
    integer               :: idx(size(A,1)), stride(size(A,1))

    l = size(A,1)

    stride(1) = 1
    do i=2,l
      stride(i) = stride(i-1)*l
    enddo ! i

    do i=0,l**l-1
      remainder = i
      do j=l,1,-1
        idx(j) = remainder / stride(j)
        remainder = remainder - idx(j)*stride(j)
      enddo ! j
      print *,A(idx+1)
    enddo ! i

  end subroutine
end module

program perm
  use perm_mod
  implicit none
  integer,parameter :: A(3) = [ 1, 2, 3 ]

  call print_permutations(A)
end program