Doubly-linked list/Definition
You are encouraged to solve this task according to the task description, using any language you may know.
Define the data structure for a complete Doubly Linked List.
- The structure should support adding elements to the head, tail and middle of the list.
- The structure should not allow circular loops
See also Linked List
ALGOL 68
<lang algol68>MODE DATA = STRING; # user defined data type #
MODE MNODE = STRUCT (
NODE pred,
succ,
DATA value
);
MODE LIST = REF MNODE; MODE NODE = REF MNODE;
STRUCT (
PROC LIST new list,
PROC (LIST)BOOL is empty,
PROC (LIST)NODE get head,
get tail,
PROC (LIST, NODE)NODE add tail,
add head,
PROC (LIST)NODE remove head,
remove tail,
PROC (LIST, NODE, NODE)NODE insert after,
PROC (LIST, NODE)NODE remove node
) class list;
new list OF class list := LIST: (
HEAP MNODE master link; master link := (master link, master link, ~); master link
);
is empty OF class list := (LIST self)BOOL:
(LIST(pred OF self) :=: LIST(self)) AND (LIST(self) :=: LIST(succ OF self));
get head OF class list := (LIST self)NODE:
succ OF self;
get tail OF class list := (LIST self)NODE:
pred OF self;
add tail OF class list := (LIST self, NODE node)NODE:
(insert after OF class list)(self, pred OF self, node);
add head OF class list := (LIST self, NODE node)NODE:
(insert after OF class list)(self, succ OF self, node);
remove head OF class list := (LIST self)NODE:
(remove node OF class list)(self, succ OF self);
remove tail OF class list := (LIST self)NODE:
(remove node OF class list)(self, pred OF self);
insert after OF class list := (LIST self, NODE cursor, NODE node)NODE: (
succ OF node := succ OF cursor; pred OF node := cursor; succ OF cursor := node; pred OF succ OF node := node; node
);
remove node OF class list := (LIST self, NODE node)NODE: (
succ OF pred OF node := succ OF node; pred OF succ OF node := pred OF node; succ OF node := pred OF node := NIL; # garbage collection hint # node
);
main: (
[]DATA sample = ("Was", "it", "a", "cat", "I", "saw");
LIST list a := new list OF class list;
NODE tmp;
IF list a :/=: REF LIST(NIL) THEN # technically "list a" is never NIL #
- Add some data to a list #
FOR i TO UPB sample DO
tmp := HEAP MNODE;
IF tmp :/=: NODE(NIL) THEN # technically "tmp" is never NIL #
value OF tmp := sample[i];
(add tail OF class list)(list a, tmp)
FI
OD;
- Iterate throught the list forward #
NODE node := (get head OF class list)(list a);
print("Iterate orward: ");
WHILE node :/=: NODE(list a) DO
print((value OF node, " "));
node := succ OF node
OD;
print(new line);
- Iterate throught the list backward #
node := (get tail OF class list)(list a);
print("Iterate backward: ");
WHILE node :/=: NODE(list a) DO
print((value OF node, " "));
node := pred OF node
OD;
print(new line);
- Finally empty the list #
print("Empty from tail: ");
WHILE NOT (is empty OF class list)(list a) DO
tmp := (remove tail OF class list)(list a);
print((value OF tmp, " "))
# sweep heap #
OD;
print(new line)
# sweep heap #
FI
)</lang> Output:
Iterate forward: Was it a cat I saw Iterate backward: saw I cat a it Was Empty from tail: saw I cat a it Was
AutoHotkey
<lang AutoHotkey>a_prev = 0 a = 1 a_next = b b_prev = a b = 2 b_next = 0 c = 4 d = 5 insert_head("c", "a") insert_tail("e", "b") insert_between("d", "a", "b") ListVars msgbox % "tail= " . tail := traverse("c") msgbox % "head= " . head := traverse("d", "reverse") return
insert_head(new, head) {
local temp %head%_prev := new %new%_prev := 0 %new%_next := head
}
insert_tail(new, tail) {
local temp %prev%_next := new %new%_prev := prev %new%_next := 0
}
insert_between(new, prev, next) {
local temp %prev%_next := new %new%_prev := prev %new%_next := next %next%_prev := new
}
traverse(element, direction="forward") { if (direction = "forward") direction = _next if (direction = "reverse") direction = _prev
name := element
MsgBox % element . "= " . %element%
name := element . direction
while, %name%
{
element := %name%
msgbox % %name% . "= " . %element%
oldname := name
name := %name% . direction
if (%oldname% == %name%)
goto circular
}
return (%oldname%) circular: msgbox % "error: list is circular: " . name . oldname . %name% . %oldname% }</lang>
C
<lang c>/* double linked list */
- include <stdio.h>
- include <stdlib.h>
struct List {
struct MNode *head; struct MNode *tail; struct MNode *tail_pred;
};
struct MNode {
struct MNode *succ; struct MNode *pred;
};
typedef struct MNode *NODE; typedef struct List *LIST;
/*
- LIST l = newList()
- create (alloc space for) and initialize a list
- /
LIST newList(void);
/*
- int isEmpty(LIST l)
- test if a list is empty
- /
int isEmpty(LIST);
/*
- NODE n = getTail(LIST l)
- get the tail node of the list, without removing it
- /
NODE getTail(LIST);
/*
- NODE n = getHead(LIST l)
- get the head node of the list, without removing it
- /
NODE getHead(LIST);
/*
- NODE rn = addTail(LIST l, NODE n)
- add the node n to the tail of the list l, and return it (rn==n)
- /
NODE addTail(LIST, NODE);
/*
- NODE rn = addHead(LIST l, NODE n)
- add the node n to the head of the list l, and return it (rn==n)
- /
NODE addHead(LIST, NODE);
/*
- NODE n = remHead(LIST l)
- remove the head node of the list and return it
- /
NODE remHead(LIST);
/*
- NODE n = remTail(LIST l)
- remove the tail node of the list and return it
- /
NODE remTail(LIST);
/*
- NODE rn = insertAfter(LIST l, NODE r, NODE n)
- insert the node n after the node r, in the list l; return n (rn==n)
- /
NODE insertAfter(LIST, NODE, NODE);
/*
- NODE rn = removeNode(LIST l, NODE n)
- remove the node n (that must be in the list l) from the list and return it (rn==n)
- /
NODE removeNode(LIST, NODE);
LIST newList(void)
{
LIST tl = malloc(sizeof(struct List));
if ( tl != NULL )
{
tl->tail_pred = (NODE)&tl->head;
tl->tail = NULL;
tl->head = (NODE)&tl->tail;
return tl;
}
return NULL;
}
int isEmpty(LIST l) {
return (l->head->succ == 0);
}
NODE getHead(LIST l) {
return l->head;
}
NODE getTail(LIST l) {
return l->tail_pred;
}
NODE addTail(LIST l, NODE n)
{
n->succ = (NODE)&l->tail; n->pred = l->tail_pred; l->tail_pred->succ = n; l->tail_pred = n; return n;
}
NODE addHead(LIST l, NODE n) {
n->succ = l->head; n->pred = (NODE)&l->head; l->head->pred = n; l->head = n; return n;
}
NODE remHead(LIST l) {
NODE h; h = l->head; l->head = l->head->succ; l->head->pred = (NODE)&l->head; return h;
}
NODE remTail(LIST l) {
NODE t; t = l->tail_pred; l->tail_pred = l->tail_pred->pred; l->tail_pred->succ = (NODE)&l->tail; return t;
}
NODE insertAfter(LIST l, NODE r, NODE n) {
n->pred = r; n->succ = r->succ; n->succ->pred = n; r->succ = n; return n;
}
NODE removeNode(LIST l, NODE n) {
n->pred->succ = n->succ; n->succ->pred = n->pred; return n;
}</lang>
Simple test:
<lang c>/* basic test */
struct IntNode {
struct MNode node; int data;
};
int main() {
int i;
LIST lista;
struct IntNode *m;
NODE n;
lista = newList();
if ( lista != NULL )
{
for(i=0; i < 5; i++)
{
m = malloc(sizeof(struct IntNode));
if ( m != NULL )
{
m->data = rand()%64;
addTail(lista, (NODE)m);
}
}
while( !isEmpty(lista) )
{
m = (struct IntNode *)remTail(lista);
printf("%d\n", m->data);
free(m);
}
free(lista);
}
}</lang>
Common Lisp
<lang lisp>(defstruct dlist head tail) (defstruct dlink content prev next)
(defun insert-between (dlist before after data)
"Insert a fresh link containing DATA after existing link BEFORE if not nil and before existing link AFTER if not nil"
(let ((new-link (make-dlink :content data :prev before :next after)))
(if (null before)
(setf (dlist-head dlist) new-link)
(setf (dlink-next before) new-link))
(if (null after)
(setf (dlist-tail dlist) new-link)
(setf (dlink-prev after) new-link))
new-link))
(defun insert-before (dlist dlink data)
"Insert a fresh link containing DATA before existing link DLINK" (insert-between dlist (dlink-prev dlink) dlink data))
(defun insert-after (dlist dlink data)
"Insert a fresh link containing DATA after existing link DLINK" (insert-between dlist dlink (dlink-next dlink) data))
(defun insert-head (dlist data)
"Insert a fresh link containing DATA at the head of DLIST" (insert-between dlist nil (dlist-head dlist) data))
(defun insert-tail (dlist data)
"Insert a fresh link containing DATA at the tail of DLIST" (insert-between dlist (dlist-tail dlist) nil data))
(defun remove-link (dlist dlink)
"Remove link DLINK from DLIST and return its content"
(let ((before (dlink-prev dlink))
(after (dlink-next dlink)))
(if (null before)
(setf (dlist-head dlist) after)
(setf (dlink-next before) after))
(if (null after)
(setf (dlist-tail dlist) before)
(setf (dlink-prev after) before))))
(defun dlist-elements (dlist)
"Returns the elements of DLIST as a list"
(labels ((extract-values (dlink acc)
(if (null dlink)
acc
(extract-values (dlink-next dlink) (cons (dlink-content dlink) acc)))))
(reverse (extract-values (dlist-head dlist) nil))))</lang>
The following produces (1 2 3 4).
<lang lisp>(let ((dlist (make-dlist)))
(insert-head dlist 1)
(insert-tail dlist 4)
(insert-after dlist (dlist-head dlist) 2)
(let* ((next-to-last (insert-before dlist (dlist-tail dlist) 3))
(bad-link (insert-before dlist next-to-last 42)))
(remove-link dlist bad-link))
(print (dlist-elements dlist)))</lang>
D
<lang d>class LinkedList(T) {
Node!(T) head, tail;
/** Iterate in the forward direction. */
int opApply (int delegate(uint, Node!(T)) dg)
{
uint i = 0;
auto link = head;
int result = 0;
while (link)
{
result = dg (i, link);
if (result) return result;
i++;
link = link.next;
}
return result;
}
static LinkedList!(T) fromArray (T[] array)
{
Node!(T) link = null;
auto head = link;
auto self = new LinkedList!(T);
foreach (elem; array)
{
link = new Node!(T)(null, link, elem, self);
if (!head)
head = link;
}
return self;
}
}
class Node(T) {
Node!(T) next;
Node!(T) previous;
LinkedList!(T) parent;
T value;
this (Node!(T) next, Node!(T) previous, T value, LinkedList!(T) parent)
in
{
assert (parent !is null);
}
body
{
this.next = next;
if (next)
next.previous = this;
if (previous)
previous.next = this;
this.previous = previous;
this.value = value;
this.parent = parent;
if (parent.head == next)
parent.head = this;
if (parent.tail == previous)
parent.tail = this;
}
/** Insert an element after this one. */
void insertAfter (T value)
{
new Node!(T)(this, next, value, parent);
}
/** Insert an element before this one. */
void insertBefore (T value)
{
new Node!(T)(previous, this, value, parent);
}
/** Remove the current node from the list. */
void remove ()
{
if (next)
next.previous = previous;
if (previous)
previous.next = next;
if (parent.tail == this)
parent.tail = previous;
if (parent.head == this)
parent.head = next;
}
}
void main () {
char[][] sample = ["was", "it", "a", "cat", "I", "saw"];
auto list = LinkedList!(char[]).fromArray (sample);
for (auto elem = list.head; elem; elem = elem.next)
{
writef ("%s ", elem.value);
if (elem.value == "it") elem.insertAfter("really");
}
writeln;
for (auto elem = list.tail; elem; elem = elem.previous)
{
writef ("%s ", elem.value);
}
writeln;
}</lang> Output:
Iterate forward: Was it really a cat I saw Iterate backward: saw I cat a really it Was Empty from tail: saw I cat a really it Was
E
<lang e>def makeDLList() {
def firstINode
def lastINode
def makeNode(var value, var prevI, var nextI) {
# To meet the requirement that the client cannot create a loop, the
# inter-node refs are protected: clients only get the external facet
# with invariant-preserving operations.
def iNode
def node { # external facet
to get() { return value }
to put(new) { value := new }
/** Return the value of the element of the list at the specified offset
from this element. */
to get(index :int) {
if (index > 0 && node.hasNext()) {
return nextI.node().get(index - 1)
} else if (index < 0 && node.hasPrev()) {
return prevI.node().get(index + 1)
} else if (index <=> 0) {
return value
} else {
throw("index out of range in dlList")
}
}
to hasPrev() {
return nextI != firstINode && nextI != null
}
to prev() {
if (!node.hasPrev()) {
throw("there is no previous node")
}
return prevI.node()
}
to hasNext() {
return nextI != lastINode && nextI != null
}
to next() {
if (!node.hasNext()) {
throw("there is no previous node")
}
return nextI.node()
}
to remove() {
if (prevI == null || nextI == null) { return }
prevI.setNextI(nextI)
nextI.setPrevI(prevI)
prevI := null
nextI := null
}
to insertAfter(newValue) {
def newI := makeNode(newValue, iNode, nextI)
nextI.setPrevI(newI)
nextI := newI
}
to insertBefore(newValue) {
prevI.node().insertAfter(newValue)
}
}
bind iNode { # internal facet
to node() { return node }
to nextI() { return nextI }
to prevI() { return prevI }
to setNextI(new) { nextI := new }
to setPrevI(new) { prevI := new }
}
return iNode
} # end makeNode
bind firstINode := makeNode(null, Ref.broken("no first prev"), lastINode)
bind lastINode := makeNode(null, firstINode, Ref.broken("no last next"))
def dlList {
to __printOn(out) {
out.print("<")
var sep := ""
for x in dlList {
out.print(sep)
out.quote(x)
sep := ", "
}
out.print(">")
}
to iterate(f) {
var n := firstINode
while (n.node().hasNext()) {
n := n.nextI()
f(n.node(), n.node()[])
}
}
to atFirst() { return firstINode.nextI().node() }
to atLast() { return lastINode.prevI().node() }
to insertFirst(new) { return firstINode.node().insertAfter(new) }
to push(new) { return lastINode.node().insertBefore(new) }
/** Return the node which has the specified value */
to nodeOf(value) {
for node => v ? (v == value) in dlList { return node }
}
}
return dlList
}</lang>
<lang e>? def list := makeDLList()
- value: <>
? list.push(1) ? list
- value: <1>
? list.push(10) ? list.push(100) ? list
- value: <1, 10, 100>
? list.atFirst().insertAfter(5) ? list
- value: <1, 5, 10, 100>
? list.insertFirst(0) ? list
- value: <0, 1, 5, 10, 100>
? list.atLast().prev().remove() ? list
- value: <0, 1, 5, 100>
? list.atLast()[] := 10 ? list
- value: <0, 1, 5, 10>
? for x in 11..20 { list.push(x) } ? list
- value: <0, 1, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20></lang>
F#
<lang fsharp>type DListAux<'T> = {mutable prev: DListAux<'T> option; data: 'T; mutable next: DListAux<'T> option} type DList<'T> = {mutable front: DListAux<'T> option; mutable back: DListAux<'T> option}
let empty() = {front=None; back=None}
let addFront dlist elt =
match dlist.front with
| None ->
let e = Some {prev=None; data=elt; next=None}
dlist.front <- e
dlist.back <- e
| Some e2 ->
let e1 = Some {prev=None; data=elt; next=Some e2}
e2.prev <- e1
dlist.front <- e1
let addBack dlist elt =
match dlist.back with
| None -> addFront dlist elt
| Some e2 ->
let e1 = Some {prev=Some e2; data=elt; next=None}
e2.next <- e1
dlist.back <- e1
let addAfter dlist link elt =
if link.next = dlist.back then addBack dlist elt else
let e = Some {prev=Some link; data=elt; next=link.next}
link.next <- e</lang>
Haskell
For an efficient implementation, see the Data.FDList module provided by liboleg. But before using doubly linked lists at all, see this discussion on Stack Overflow.
<lang haskell>import qualified Data.Map as M
type NodeID = Maybe Rational data Node a = Node
{vNode :: a,
pNode, nNode :: NodeID}
type DLList a = M.Map Rational (Node a)
empty = M.empty
singleton a = M.singleton 0 $ Node a Nothing Nothing
fcons :: a -> DLList a -> DLList a fcons a list | M.null list = singleton a
| otherwise = M.insert newid new $
M.insert firstid changed list
where (firstid, Node firstval _ secondid) = M.findMin list
newid = firstid - 1
new = Node a Nothing (Just firstid)
changed = Node firstval (Just newid) secondid
rcons :: a -> DLList a -> DLList a rcons a list | M.null list = singleton a
| otherwise = M.insert lastid changed $
M.insert newid new list
where (lastid, Node lastval penultimateid _) = M.findMax list
newid = lastid + 1
changed = Node lastval penultimateid (Just newid)
new = Node a (Just lastid) Nothing
mcons :: a -> Node a -> Node a -> DLList a -> DLList a mcons a n1 n2 = M.insert n1id left .
M.insert midid mid . M.insert n2id right
where Node n1val farleftid (Just n2id) = n1
Node n2val (Just n1id) farrightid = n2
midid = (n1id + n2id) / 2 -- Hence the use of Rationals.
mid = Node a (Just n1id) (Just n2id)
left = Node n1val farleftid (Just midid)
right = Node n2val (Just midid) farrightid
firstNode :: DLList a -> Node a firstNode = snd . M.findMin
lastNode :: DLList a -> Node a lastNode = snd . M.findMax
nextNode :: DLList a -> Node a -> Maybe (Node a) nextNode l n = nNode n >>= flip M.lookup l
prevNode :: DLList a -> Node a -> Maybe (Node a) prevNode l n = pNode n >>= flip M.lookup l
fromList = foldr fcons empty
toList = map vNode . M.elems</lang>
An example of use:
<lang haskell>main = putStrLn $ toList l
where l = mcons 'M' n1 n2 x
x = rcons 'Z' $ fcons 'a' $ fcons 'q' $ singleton 'w'
n1 = firstNode x
Just n2 = nextNode x n1</lang>
JavaScript
See Doubly-Linked List (element)#JavaScript, Doubly-Linked List (element insertion)#JavaScript and Doubly-Linked List (traversal)#JavaScript
Python
In the high level language Python, its list native datatype should be used. It automatically preserves the integrity of the list w.r.t. loops and allows insertion at any point using list.insert() via an integer index into the list rather than a machine-code level pointer to a list element.
Ruby
See Doubly-Linked List (element)#Ruby, Doubly-Linked List (element insertion)#Ruby and Doubly-Linked List (traversal)#Ruby
Tcl
This task was earlier marked as unfeasible for Tcl. Tcl lists are compact arrays of pointers to values. However, on very long lists, insertions and deletions (if not at end) may require copying a large amount of data. In such cases, the implementation below may be helpful. It provides a single dl command, which is called with the name of a DList, a method name, and possibly more arguments as required. The testcases below should give a good idea. The asList and asList2 methods demonstrate forward and backward traversal.
See also Doubly-Linked List (element) for a TclOO-based version.
<lang Tcl>package require Tcl 8.4 proc dl {_name cmd {where error} {value ""}} {
upvar 1 $_name N
switch -- $cmd {
insert {
if ![info exists N()] {set N() {"" "" 0}}
set id [lindex $N() 2]
lset N() 2 [incr id]
switch -- $where {
head {
set prev {}
set next [lindex $N() 0]
lset N() 0 $id
}
end {
set prev [lindex $N() 1]
set next {}
lset N() 1 $id
}
default {
set prev $where
set next [lindex $N($where) 1]
lset N($where) 1 $id
}
}
if {$prev ne ""} {lset N($prev) 1 $id}
if {$next ne ""} {lset N($next) 0 $id}
if {[lindex $N() 1] eq ""} {lset N() 1 $id}
set N($id) [list $prev $next $value]
return $id
}
delete {
set i $where
if {$where eq "head"} {set i [dl N head]}
if {$where eq "end"} {set i [dl N end]}
foreach {prev next} $N($i) break
if {$prev ne ""} {lset N($prev) 1 $next}
if {$next ne ""} {lset N($next) 0 $prev}
if {[dl N head] == $i} {lset N() 0 $next}
if {[dl N end] == $i} {lset N() 1 $prev}
unset N($i)
}
findfrom {
if {$where eq "head"} {set where [dl N head]}
for {set i $where} {$i ne ""} {set i [dl N next $i]} {
if {[dl N get $i] eq $value} {return $i}
}
}
get {lindex $N($where) 2}
set {lset N($where) 2 $value; set value}
head {lindex $N() 0}
end {lindex $N() 1}
next {lindex $N($where) 1}
prev {lindex $N($where) 0}
length {expr {[array size N]-1}}
asList {
set res {}
for {set i [dl N head]} {$i ne ""} {set i [dl N next $i]} {
lappend res [dl N get $i]
}
return $res
}
asList2 {
set res {}
for {set i [dl N end]} {$i ne ""} {set i [dl N prev $i]} {
lappend res [dl N get $i]
}
return $res
}
}
}</lang> <lang tcl># Testing code set testcases [split {
dl D insert head foo dl D insert end bar dl D insert head hello dl D set [dl D head] hi dl D insert end grill set i [dl D findfrom head bar] dl D set $i BAR dl D insert $i and dl D length dl D asList2 dl D delete $i dl D findfrom head nix dl D delete head dl D delete end dl D delete end dl D delete head dl D length
} \n] foreach case $testcases {
if {[string trim $case] ne ""} {
puts " $case -> [eval $case] : [dl D asList]"
if {[lsearch $argv -p] >= 0} {parray D}
}
}</lang>
Visual Basic .NET
<lang vbnet>Public Class DoubleLinkList(Of T)
Private m_Head As Node(Of T) Private m_Tail As Node(Of T)
Public Sub AddHead(ByVal value As T)
Dim node As New Node(Of T)(Me, value)
If m_Head Is Nothing Then
m_Head = Node
m_Tail = m_Head
Else
node.Next = m_Head
m_Head = node
End If
End Sub
Public Sub AddTail(ByVal value As T)
Dim node As New Node(Of T)(Me, value)
If m_Tail Is Nothing Then
m_Head = node
m_Tail = m_Head
Else
node.Previous = m_Tail
m_Tail = node
End If
End Sub
Public ReadOnly Property Head() As Node(Of T)
Get
Return m_Head
End Get
End Property
Public ReadOnly Property Tail() As Node(Of T)
Get
Return m_Tail
End Get
End Property
Public Sub RemoveTail()
If m_Tail Is Nothing Then Return
If m_Tail.Previous Is Nothing Then 'empty
m_Head = Nothing
m_Tail = Nothing
Else
m_Tail = m_Tail.Previous
m_Tail.Next = Nothing
End If
End Sub
Public Sub RemoveHead()
If m_Head Is Nothing Then Return
If m_Head.Next Is Nothing Then 'empty
m_Head = Nothing
m_Tail = Nothing
Else
m_Head = m_Head.Next
m_Head.Previous = Nothing
End If
End Sub
End Class
Public Class Node(Of T)
Private ReadOnly m_Value As T Private m_Next As Node(Of T) Private m_Previous As Node(Of T) Private ReadOnly m_Parent As DoubleLinkList(Of T)
Public Sub New(ByVal parent As DoubleLinkList(Of T), ByVal value As T)
m_Parent = parent
m_Value = value
End Sub
Public Property [Next]() As Node(Of T)
Get
Return m_Next
End Get
Friend Set(ByVal value As Node(Of T))
m_Next = value
End Set
End Property
Public Property Previous() As Node(Of T)
Get
Return m_Previous
End Get
Friend Set(ByVal value As Node(Of T))
m_Previous = value
End Set
End Property
Public ReadOnly Property Value() As T
Get
Return m_Value
End Get
End Property
Public Sub InsertAfter(ByVal value As T)
If m_Next Is Nothing Then
m_Parent.AddTail(value)
ElseIf m_Previous Is Nothing Then
m_Parent.AddHead(value)
Else
Dim node As New Node(Of T)(m_Parent, value)
node.Previous = Me
node.Next = Me.Next
Me.Next.Previous = node
Me.Next = node
End If
End Sub
Public Sub Remove()
If m_Next Is Nothing Then
m_Parent.RemoveTail()
ElseIf m_Previous Is Nothing Then
m_Parent.RemoveHead()
Else
m_Previous.Next = Me.Next
m_Next.Previous = Me.Previous
End If
End Sub
End Class</lang>