clear_hash_table Subroutine

    pure subroutine clear_hash_table(hash_table)

        ! Take hash_table and clear it. This is done by nullifying all pointers
        ! in all the linked lists that form the hash table, and setting the
        ! first index to zero.

        type(ll_node), pointer, intent(inout) :: hash_table(:)
        type(ll_node), pointer :: curr, prev
        integer :: i

        ! Loop over all entries corresponding to different hash values.
        do i = 1, size(hash_table)
            ! Point to the second entry in this linked list.
            curr => hash_table(i)%next
            ! Point to the first entry in this linked list.
            prev => hash_table(i)
            ! Set the first index to zero.
            prev%ind = 0
            nullify (prev%next)
            ! Loop over the whole linked list and deallocate all pointers.
            do while (associated(curr))
                prev => curr
                curr => curr%next
                deallocate(prev)
            end do
        end do

        nullify (curr)
        nullify (prev)

    end subroutine clear_hash_table