Fortran递归选择排序可分配单向链表实现问题求助

任务要求：实现可分配递归单向链表的选择排序，按姓氏字母顺序排序，排序步骤为：

• 找到链表中姓氏最小的节点；
• 将该节点从原位置移除并填补空缺（例如将 A -> minimum -> B -> C 变为 A -> B -> C）；
• 将该节点放到链表头部（例如变为 minimum -> A -> B -> C）。

目前遇到的问题：已编写代码，但无法正确将最小节点移到链表头部。尝试的节点移动方法仅能处理单个元素，无法保留后续链表关联。已耗时40多小时调试仍无进展，虽认为RemoveNode子程序正确，但也不排除问题出在此处。

代码片段 #

ChooseAndPaste子程序 #

22    recursive subroutine ChooseAndPaste(unsorted, minimum, current)
23       type(SourceLine), allocatable :: unsorted
24       type(SourceLine), allocatable :: minimum 
25       type(SourceLine), allocatable :: current 
26       type(SourceLine), allocatable :: temp
27          if (allocated(current)) then
28       print *, "makr 3 ", current%field
29             if (current%field < minimum%field) then
30                call ChooseAndPaste(unsorted, current, current%next)
31             else
32                call ChooseAndPaste(unsorted, minimum, current%next)
33             end if
34          else 
35          if ((allocated(unsorted) .and. allocated(minimum) .and. (unsorted%field /= minimum%field))) then
36             print *, minimum%field
37             call RemoveNode(unsorted, minimum)
38 !            call move_alloc(unsorted, temp)
39 !            call move_alloc(minimum, unsorted)
40 !            call move_alloc(temp, unsorted%next)
41          end if
42       end if
43    end subroutine ChooseAndPaste

注释38-40行时，结果接近有序，但无法将最小节点添加到链表头部。38-40行的方法仅移动顶层元素，无法保留后续关联。

SelectionSort上层调用子程序 #

recursive subroutine SelectionSort(unsorted)
11    type(SourceLine), allocatable :: unsorted
12    
13       if (allocated(unsorted)) then
14          call ChooseAndPaste(unsorted, unsorted, unsorted%next) 
15     
16          if (.not. allocated(unsorted)) return ! <-- this line was added because of this issue
17          call SelectionSort(unsorted%next) 
18       end if
19
20    end subroutine SelectionSort

数据结构定义 #

type SourceLine
      character(:, CH_), allocatable   :: field
      type(SourceLine), allocatable    :: Next
   end type SourceLine

RemoveNode子程序 #

46    recursive subroutine RemoveNode(unsorted, minimum)
47       type(SourceLine), allocatable :: unsorted
48       type(SourceLine), allocatable :: minimum
49       type(SourceLine), allocatable :: Temp
50
51
52       if (.not. allocated(unsorted)) return
53
54       ! Check if current node is the target
55       if (unsorted%field == minimum%field) then
56           if (allocated(unsorted%next)) then
57               ! Keep the rest of the list
58               call move_alloc(unsorted%next, Temp)
59               call move_alloc(Temp, unsorted)
60           else
61               ! This was the last node
62               deallocate(unsorted)
63               print *, "mark 1"
64           end if
65           return
66       end if
67       ! Recursively check next nodes
68     if (allocated(unsorted%next)) then
69         call RemoveNode(unsorted%next, minimum)
70      end if
71    end subroutine RemoveNode

个人判断：认为RemoveNode子程序正确，但也不排除存在问题的可能。

内容的提问来源于stack exchange，提问作者NikPlayAnon