Linked Structures

Delete by Value

Find the node before the target value and rewire its next pointer so the target node leaves the chain.

Algorithm

The replay labels nodes by value, such as node(20), and never exposes object identity or memory addresses. This Fortran DSA implementation uses the same small chain as the rest of the DSA track.

Basic Implementation

basic.f90 
program linked_list_lesson
    implicit none
    type :: list_node
        integer :: value
        type(list_node), pointer :: next => null()
    end type list_node
    type(list_node), pointer :: head, cursor, new_head
    type(list_node), pointer :: n1, n2, n3, n4

    allocate(n1); n1%value = 10
    allocate(n2); n2%value = 20
    allocate(n3); n3%value = 30
    allocate(n4); n4%value = 40
    n1%next => n2; n2%next => n3; n3%next => n4; n4%next => null()
    head => n1
    cursor => head
    do while (associated(cursor%next))
        if (cursor%next%value == 30) then
            cursor%next => cursor%next%next
            exit
        end if
        cursor => cursor%next
    end do
    call print_chain(head)
contains
    subroutine print_chain(start)
        type(list_node), pointer :: start
        type(list_node), pointer :: cur
        cur => start
        do while (associated(cur))
            write(*, '(I0,A)', advance='no') cur%value, ' -> '
            cur => cur%next
        end do
        write(*, '(A)') 'null'
    end subroutine print_chain
end program linked_list_lesson

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Keep the explicit node and pointer/reference operations; array shortcuts hide the linked-list state this lesson is meant to replay.
  • The final output prints the chain in a deterministic a -> b -> null form for cross-language comparison.
predecessor Deletion needs the node before the one being removed.
rewiring The predecessor skips the target and points at the target's next node.