面试题：Fortran复杂数据类型定义下的自定义数据结构操作

Question

定义一个描述书籍信息的派生类型，包含书名（字符型）、作者（字符型）、出版年份（整数）、价格（实数）等成员。基于此派生类型，创建一个链表数据结构，实现链表节点的插入、删除和查找操作，用Fortran代码实现。

Answer 1

module book_module
    type book_type
        character(len=100) :: title
        character(len=50) :: author
        integer :: year
        real :: price
    end type book_type
    type node_type
        type(book_type) :: data
        type(node_type), pointer :: next
    end type node_type
contains
    subroutine insert_node(head, new_book)
        type(node_type), pointer :: head
        type(book_type), intent(in) :: new_book
        type(node_type), pointer :: new_node, current
        allocate(new_node)
        new_node%data = new_book
        new_node%next => null()
        if (.not. associated(head)) then
            head => new_node
        else
            current => head
            do while (associated(current%next))
                current => current%next
            end do
            current%next => new_node
        end if
    end subroutine insert_node
    subroutine delete_node(head, target_title)
        type(node_type), pointer :: head
        character(len=100), intent(in) :: target_title
        type(node_type), pointer :: current, prev
        current => head
        prev => null()
        do while (associated(current))
            if (current%data%title == target_title) then
                if (.not. associated(prev)) then
                    head => current%next
                else
                    prev%next => current%next
                end if
                deallocate(current)
                return
            end if
            prev => current
            current => current%next
        end do
    end subroutine delete_node
    subroutine find_node(head, target_title, found_book)
        type(node_type), pointer :: head
        character(len=100), intent(in) :: target_title
        type(book_type), intent(out) :: found_book
        type(node_type), pointer :: current
        current => head
        do while (associated(current))
            if (current%data%title == target_title) then
                found_book = current%data
                return
            end if
            current => current%next
        end do
        found_book%title = ''
        found_book%author = ''
        found_book%year = 0
        found_book%price = 0.0
    end subroutine find_node
end module book_module

program main
    use book_module
    implicit none
    type(node_type), pointer :: head => null()
    type(book_type) :: new_book, found_book
    new_book%title = 'Fortran Programming'
    new_book%author = 'John Doe'
    new_book%year = 2020
    new_book%price = 30.0
    call insert_node(head, new_book)
    call find_node(head, 'Fortran Programming', found_book)
    if (found_book%title /= '') then
        write(*,*) 'Book found:'
        write(*,*) 'Title:', found_book%title
        write(*,*) 'Author:', found_book%author
        write(*,*) 'Year:', found_book%year
        write(*,*) 'Price:', found_book%price
    else
        write(*,*) 'Book not found.'
    end if
    call delete_node(head, 'Fortran Programming')
    call find_node(head, 'Fortran Programming', found_book)
    if (found_book%title /= '') then
        write(*,*) 'Book found after deletion (should not happen).'
    else
        write(*,*) 'Book not found after deletion (correct).'
    end if
end program main