Doubly-linked list/Traversal
Traverse from the beginning of a doubly-linked list to the end, and from the end to the beginning.
You are encouraged to solve this task according to the task description, using any language you may know.
- See also
- Array
- Associative array: Creation, Iteration
- Collections
- Compound data type
- Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
- Linked list
- Queue: Definition, Usage
- Set
- Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
- Stack
Ada
<lang Ada>with Ada.Containers.Doubly_Linked_Lists; with Ada.Text_IO;
procedure Traversing is
package Char_Lists is new Ada.Containers.Doubly_Linked_Lists (Character);
procedure Print (Position : in Char_Lists.Cursor) is
begin
Ada.Text_IO.Put (Char_Lists.Element (Position));
end Print;
My_List : Char_Lists.List;
begin
My_List.Append ('R');
My_List.Append ('o');
My_List.Append ('s');
My_List.Append ('e');
My_List.Append ('t');
My_List.Append ('t');
My_List.Append ('a');
My_List.Iterate (Print'Access); Ada.Text_IO.New_Line;
My_List.Reverse_Iterate (Print'Access); Ada.Text_IO.New_Line;
end Traversing;</lang>
ALGOL 68
LinkedList.alg:<lang algol68># Node struct - contains next and prev NODE pointers and DATA # MODE NODE = STRUCT(
DATA data, REF NODE prev, REF NODE next );
- List structure - contains head and tail NODE pointers #
MODE LIST = STRUCT(
REF NODE head, REF NODE tail );
- --- PREPEND - Adds a node to the beginning of the list ---#
PRIO PREPEND = 1; OP PREPEND = (REF LIST list, DATA data) VOID: (
HEAP NODE n := (data, NIL, NIL);
IF head OF list IS REF NODE(NIL) THEN
head OF list := tail OF list := n
ELSE
next OF n := head OF list;
prev OF head OF list := head OF list := n
FI
);
- --- APPEND - Adds a node to the end of the list ---#
PRIO APPEND = 1; OP APPEND = (REF LIST list, DATA data) VOID: (
HEAP NODE n := (data, NIL, NIL);
IF head OF list IS REF NODE(NIL) THEN
head OF list := tail OF list := n
ELSE
prev OF n := tail OF list;
next OF tail OF list := tail OF list := n
FI
);
- --- REMOVE_FIRST - removes & returns node at end of the list ---#
PRIO REMOVE_FIRST = 1; OP REMOVE_FIRST = (REF LIST list) DATA: (
IF head OF list ISNT REF NODE(NIL) THEN
DATA d := data OF head OF list;
prev OF next OF head OF list := NIL;
head OF list := next OF head OF list;
d # return d #
FI
);
- --- REMOVE_LAST: removes & returns node at front of list --- #
PRIO REMOVE_LAST = 1; OP REMOVE_LAST = (REF LIST list) DATA: (
IF head OF list ISNT REF NODE(NIL) THEN
DATA d := data OF tail OF list;
next OF prev OF tail OF list := NIL;
tail OF list := prev OF tail OF list;
d # return d #
FI
);
- --- PURGE - removes all elements from the list ---#
PRIO PURGE = 2; OP PURGE = (REF LIST list) VOID: (
head OF list := tail OF list := NIL
);
- --- returns the data at the end of the list ---#
PRIO LAST_IN = 2; OP LAST_IN = (REF LIST list) DATA: (
IF head OF list ISNT REF NODE(NIL) THEN
data OF tail OF list
FI
);
- --- returns the data at the front of the list ---#
PRIO FIRST_IN = 2; OP FIRST_IN = (REF LIST list) DATA: (
IF head OF list ISNT REF NODE(NIL) THEN
data OF head OF list
FI
);
- --- Traverses through the list forwards ---#
PROC forward traversal = (LIST list) VOID: (
REF NODE travel := head OF list;
WHILE travel ISNT REF NODE(NIL) DO
list visit(data OF travel);
travel := next OF travel
OD
);
- --- Traverses through the list backwards ---#
PROC backward traversal = (LIST list) VOID: (
REF NODE travel := tail OF list;
WHILE travel ISNT REF NODE(NIL) DO
list visit(data OF travel);
travel := prev OF travel
OD
)</lang>
main.alg:<lang algol68>PR READ "LinkedList.alg" PR;
MODE EMPLOYEE = STRUCT(STRING name, INT salary, INT years); MODE DATA = EMPLOYEE; #Sets the data type that is in the list#
- Function that traversals call for each node in list #
PROC list visit = (REF DATA data) VOID: (
print((
"EMPLOYEE NAME : ", name OF data , newline,
" SALARY: " , salary OF data, newline,
" YEARS : " , years OF data, newline
))
);
main: (
EMPLOYEE empl; name OF empl := "one"; salary OF empl := 100; years OF empl := 10; LIST list := (NIL, NIL);
list PREPEND empl; name OF empl := "two"; salary OF empl := 200; years OF empl := 20; list APPEND empl; name OF empl := "three"; salary OF empl := 300; years OF empl := 30; list APPEND empl; salary OF empl := 400; years OF empl := 40; name OF empl := "four"; list APPEND empl;
forward traversal(list); PURGE list; forward traversal(list)
)</lang>
- Output:
EMPLOYEE NAME : one
SALARY: +100
YEARS : +10
EMPLOYEE NAME : two
SALARY: +200
YEARS : +20
EMPLOYEE NAME : three
SALARY: +300
YEARS : +30
EMPLOYEE NAME : four
SALARY: +400
YEARS : +40
ARM Assembly
<lang ARM Assembly> /* ARM assembly Raspberry PI */ /* program transDblList.s */ /* REMARK 1 : this program use routines in a include file
see task Include a file language arm assembly for the routine affichageMess conversion10S see at end of this program the instruction include */
/* Constantes */ .equ STDOUT, 1 @ Linux output console .equ EXIT, 1 @ Linux syscall .equ READ, 3 .equ WRITE, 4
/*******************************************/ /* Structures */ /********************************************/ /* structure Doublylinkedlist*/
.struct 0
dllist_head: @ head node
.struct dllist_head + 4
dllist_tail: @ tail node
.struct dllist_tail + 4
dllist_fin: /* structure Node Doublylinked List*/
.struct 0
NDlist_next: @ next element
.struct NDlist_next + 4
NDlist_prev: @ previous element
.struct NDlist_prev + 4
NDlist_value: @ element value or key
.struct NDlist_value + 4
NDlist_fin: /* Initialized data */ .data szMessInitListe: .asciz "List initialized.\n" szMessListInv: .asciz "Display list inverse :\n" szCarriageReturn: .asciz "\n" szMessErreur: .asciz "Error detected.\n" /* datas message display */ szMessResult: .ascii "Result value :" sValue: .space 12,' '
.asciz "\n"
/* UnInitialized data */ .bss dllist1: .skip dllist_fin @ list memory place
/* code section */ .text .global main main:
ldr r0,iAdrdllist1 bl newDList @ create new list ldr r0,iAdrszMessInitListe bl affichageMess ldr r0,iAdrdllist1 @ list address mov r1,#10 @ value bl insertHead @ insertion at head cmp r0,#-1 beq 99f ldr r0,iAdrdllist1 mov r1,#20 bl insertTail @ insertion at tail cmp r0,#-1 beq 99f ldr r0,iAdrdllist1 @ list address mov r1,#10 @ value to after insered mov r2,#15 @ new value bl insertAfter cmp r0,#-1 beq 99f ldr r0,iAdrdllist1 @ list address mov r1,#20 @ value to after insered mov r2,#25 @ new value bl insertAfter cmp r0,#-1 beq 99f ldr r0,iAdrdllist1 bl transHeadTail @ display value head to tail ldr r0,iAdrszMessListInv bl affichageMess ldr r0,iAdrdllist1 bl transTailHead @ display value tail to head b 100f
99:
ldr r0,iAdrszMessErreur bl affichageMess
100: @ standard end of the program
mov r7, #EXIT @ request to exit program svc 0 @ perform system call
iAdrszMessInitListe: .int szMessInitListe iAdrszMessErreur: .int szMessErreur iAdrszMessListInv: .int szMessListInv iAdrszCarriageReturn: .int szCarriageReturn iAdrdllist1: .int dllist1 /******************************************************************/ /* create new list */ /******************************************************************/ /* r0 contains the address of the list structure */ newDList:
push {r1,lr} @ save registers
mov r1,#0
str r1,[r0,#dllist_tail]
str r1,[r0,#dllist_head]
pop {r1,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* list is empty ? */ /******************************************************************/ /* r0 contains the address of the list structure */ /* r0 return 0 if empty else return 1 */ isEmpty:
//push {r1,lr} @ save registers
ldr r0,[r0,#dllist_head]
cmp r0,#0
movne r0,#1
//pop {r1,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* insert value at list head */ /******************************************************************/ /* r0 contains the address of the list structure */ /* r1 contains value */ insertHead:
push {r1-r4,lr} @ save registers
mov r4,r0 @ save address
mov r0,r1 @ value
bl createNode
cmp r0,#-1 @ allocation error ?
beq 100f
ldr r2,[r4,#dllist_head] @ load address first node
str r2,[r0,#NDlist_next] @ store in next pointer on new node
mov r1,#0
str r1,[r0,#NDlist_prev] @ store zero in previous pointer on new node
str r0,[r4,#dllist_head] @ store address new node in address head list
cmp r2,#0 @ address first node is null ?
strne r0,[r2,#NDlist_prev] @ no store adresse new node in previous pointer
streq r0,[r4,#dllist_tail] @ else store new node in tail address
100:
pop {r1-r4,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* insert value at list tail */ /******************************************************************/ /* r0 contains the address of the list structure */ /* r1 contains value */ insertTail:
push {r1-r4,lr} @ save registers
mov r4,r0 @ save list address
mov r0,r1 @ value
bl createNode @ new node
cmp r0,#-1
beq 100f @ allocation error
ldr r2,[r4,#dllist_tail] @ load address last node
str r2,[r0,#NDlist_prev] @ store in previous pointer on new node
mov r1,#0 @ store null un next pointer
str r1,[r0,#NDlist_next]
str r0,[r4,#dllist_tail] @ store address new node on list tail
cmp r2,#0 @ address last node is null ?
strne r0,[r2,#NDlist_next] @ no store address new node in next pointer
streq r0,[r4,#dllist_head] @ else store in head list
100:
pop {r1-r4,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* insert value after other element */ /******************************************************************/ /* r0 contains the address of the list structure */ /* r1 contains value to search*/ /* r2 contains value to insert */ insertAfter:
push {r1-r5,lr} @ save registers
mov r4,r0
bl searchValue @ search node with this value in r1
cmp r0,#-1
beq 100f @ not found -> error
mov r5,r0 @ save address of node find
mov r0,r2 @ new value
bl createNode @ create new node
cmp r0,#-1
beq 100f @ allocation error
ldr r2,[r5,#NDlist_next] @ load pointer next of find node
str r0,[r5,#NDlist_next] @ store new node in pointer next
str r5,[r0,#NDlist_prev] @ store address find node in previous pointer on new node
str r2,[r0,#NDlist_next] @ store pointer next of find node on pointer next on new node
cmp r2,#0 @ next pointer is null ?
strne r0,[r2,#NDlist_prev] @ no store address new node in previous pointer
streq r0,[r4,#dllist_tail] @ else store in list tail
100:
pop {r1-r5,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* search value */ /******************************************************************/ /* r0 contains the address of the list structure */ /* r1 contains the value to search */ /* r0 return address of node or -1 if not found */ searchValue:
push {r2,lr} @ save registers
ldr r0,[r0,#dllist_head] @ load first node
1:
cmp r0,#0 @ null -> end search not found moveq r0,#-1 beq 100f ldr r2,[r0,#NDlist_value] @ load node value cmp r2,r1 @ equal ? beq 100f ldr r0,[r0,#NDlist_next] @ load addresse next node b 1b @ and loop
100:
pop {r2,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* transversal for head to tail */ /******************************************************************/ /* r0 contains the address of the list structure */ transHeadTail:
push {r2,lr} @ save registers
ldr r2,[r0,#dllist_head] @ load first node
1:
ldr r0,[r2,#NDlist_value] ldr r1,iAdrsValue bl conversion10S ldr r0,iAdrszMessResult bl affichageMess ldr r2,[r2,#NDlist_next] cmp r2,#0 bne 1b
100:
pop {r2,lr} @ restaur registers
bx lr @ return
iAdrszMessResult: .int szMessResult iAdrsValue: .int sValue /******************************************************************/ /* transversal for tail to head */ /******************************************************************/ /* r0 contains the address of the list structure */ transTailHead:
push {r2,lr} @ save registers
ldr r2,[r0,#dllist_tail] @ load last node
1:
ldr r0,[r2,#NDlist_value] ldr r1,iAdrsValue bl conversion10S ldr r0,iAdrszMessResult bl affichageMess ldr r2,[r2,#NDlist_prev] cmp r2,#0 bne 1b
100:
pop {r2,lr} @ restaur registers
bx lr @ return
/******************************************************************/ /* Create new node */ /******************************************************************/ /* r0 contains the value */ /* r0 return node address or -1 if allocation error*/ createNode:
push {r1-r7,lr} @ save registers
mov r4,r0 @ save value
@ allocation place on the heap
mov r0,#0 @ allocation place heap
mov r7,#0x2D @ call system 'brk'
svc #0
mov r5,r0 @ save address heap for output string
add r0,#NDlist_fin @ reservation place one element
mov r7,#0x2D @ call system 'brk'
svc #0
cmp r0,#-1 @ allocation error
beq 100f
mov r0,r5
str r4,[r0,#NDlist_value] @ store value
mov r2,#0
str r2,[r0,#NDlist_next] @ store zero to pointer next
str r2,[r0,#NDlist_prev] @ store zero to pointer previous
100:
pop {r1-r7,lr} @ restaur registers
bx lr @ return
/***************************************************/ /* ROUTINES INCLUDE */ /***************************************************/ .include "../affichage.inc"
</lang>
AutoHotkey
Axe
<lang axe>LINK(L₁,1)→A LINK(L₁+10,2)→B LINK(L₁+50,3)→C
INSERT(A,B) INSERT(A,C)
A→I While I≠0
Disp VALUE(I)▶Dec,i NEXT(I)→I
End
Disp "-----",i
B→I While I≠0
Disp VALUE(I)▶Dec,i PREV(I)→I
End</lang>
BBC BASIC
<lang bbcbasic> DIM node{pPrev%, pNext%, iData%}
DIM a{} = node{}, b{} = node{}, c{} = node{}
a.pNext% = b{}
a.iData% = 123
b.pPrev% = a{}
b.iData% = 789
c.iData% = 456
PROCinsert(a{}, c{})
PRINT "Traverse forwards:"
pnode% = a{}
REPEAT
!(^node{}+4) = pnode%
PRINT node.iData%
pnode% = node.pNext%
UNTIL pnode% = 0
PRINT "Traverse backwards:"
pnode% = b{}
REPEAT
!(^node{}+4) = pnode%
PRINT node.iData%
pnode% = node.pPrev%
UNTIL pnode% = 0
END
DEF PROCinsert(here{}, new{})
LOCAL temp{} : DIM temp{} = node{}
new.pNext% = here.pNext%
new.pPrev% = here{}
!(^temp{}+4) = new.pNext%
temp.pPrev% = new{}
here.pNext% = new{}
ENDPROC
</lang> Output:
Traverse forwards:
123
456
789
Traverse backwards:
789
456
123
C
<lang c>// A doubly linked list of strings;
- include <stdio.h>
- include <stdlib.h>
- include <string.h>
typedef struct sListEntry {
const char *value; struct sListEntry *next; struct sListEntry *prev;
} *ListEntry, *LinkedList;
typedef struct sListIterator{
ListEntry link; LinkedList head;
} *LIterator;
LinkedList NewList() {
ListEntry le = malloc(sizeof(struct sListEntry));
if (le) {
le->value = NULL;
le->next = le->prev = NULL;
}
return le;
}
int LL_Append(LinkedList ll, const char *newVal) {
ListEntry le = malloc(sizeof(struct sListEntry));
if (le) {
le->value = strdup(newVal);
le->prev = ll->prev;
le->next = NULL;
if (le->prev)
le->prev->next = le;
else
ll->next = le;
ll->prev = le;
}
return (le!= NULL);
}
int LI_Insert(LIterator iter, const char *newVal) {
ListEntry crnt = iter->link;
ListEntry le = malloc(sizeof(struct sListEntry));
if (le) {
le->value = strdup(newVal);
if ( crnt == iter->head) {
le->prev = NULL;
le->next = crnt->next;
crnt->next = le;
if (le->next)
le->next->prev = le;
else
crnt->prev = le;
}
else {
le->prev = ( crnt == NULL)? iter->head->prev : crnt->prev;
le->next = crnt;
if (le->prev)
le->prev->next = le;
else
iter->head->next = le;
if (crnt)
crnt->prev = le;
else
iter->head->prev = le;
}
}
return (le!= NULL);
}
LIterator LL_GetIterator(LinkedList ll ) {
LIterator liter = malloc(sizeof(struct sListIterator)); liter->head = ll; liter->link = ll; return liter;
}
- define LLI_Delete( iter ) \
{free(iter); \
iter = NULL;}
int LLI_AtEnd(LIterator iter) {
return iter->link == NULL;
} const char *LLI_Value(LIterator iter) {
return (iter->link)? iter->link->value: NULL;
} int LLI_Next(LIterator iter) {
if (iter->link) iter->link = iter->link->next; return(iter->link != NULL);
} int LLI_Prev(LIterator iter) {
if (iter->link) iter->link = iter->link->prev; return(iter->link != NULL);
}
int main() {
static const char *contents[] = {"Read", "Orage", "Yeller",
"Glean", "Blew", "Burple"};
int ix;
LinkedList ll = NewList(); //new linked list
LIterator iter;
for (ix=0; ix<6; ix++) //insert contents
LL_Append(ll, contents[ix]);
iter = LL_GetIterator(ll); //get an iterator
printf("forward\n");
while(LLI_Next(iter)) //iterate forward
printf("value=%s\n", LLI_Value(iter));
LLI_Delete(iter); //delete iterator
printf("\nreverse\n");
iter = LL_GetIterator(ll);
while(LLI_Prev(iter)) //iterate reverse
printf("value=%s\n", LLI_Value(iter));
LLI_Delete(iter);
//uhhh-- delete list??
return 0;
}</lang>
C#
<lang csharp>using System; using System.Collections.Generic;
namespace RosettaCode.DoublyLinkedList {
internal static class Program
{
private static void Main()
{
var list = new LinkedList<char>("hello");
var current = list.First;
do
{
Console.WriteLine(current.Value);
} while ((current = current.Next) != null);
Console.WriteLine();
current = list.Last;
do
{
Console.WriteLine(current.Value);
} while ((current = current.Previous) != null);
}
}
}</lang> Output:
h e l l o o l l e h
C++
<lang cpp>#include <iostream>
- include <list>
int main () {
std::list<int> numbers {1, 5, 7, 0, 3, 2};
for(const auto& i: numbers)
std::cout << i << ' ';
std::cout << '\n';
}</lang>
- Output:
1 5 7 0 3 2
Clojure
Given the definition in Doubly-linked list/Definition#Clojure, <lang Clojure>(def dl (double-list [:a :b :c :d]))
- => #'user/dl
((juxt seq rseq) dl)
- => [(
- a :b :c :d) (:d :c :b :a)]
(take-while identity (iterate get-next (get-head dl)))
- => (#
- double_list.Node{:prev nil, :next #<Object...>, :data :a, :key #<Object...>}
- => #
- double_list.Node{:prev #<Object...>, :next #<Object...>, :data :b, :key #<Object...>}
- => #
- double_list.Node{:prev #<Object...>, :next #<Object...>, :data :c, :key #<Object...>}
- => #
- double_list.Node{:prev #<Object...>, :next nil, :data :d, :key #<Object...>})
(take-while identity (iterate get-prev (get-tail dl)))
- => (#
- double_list.Node{:prev #<Object...>, :next nil, :data :d, :key #<Object...>}
- => #
- double_list.Node{:prev #<Object...>, :next #<Object...>, :data :c, :key #<Object...>}
- => #
- double_list.Node{:prev #<Object...>, :next #<Object...>, :data :b, :key #<Object...>}
- => #
- double_list.Node{:prev nil, :next #<Object...>, :data :a, :key #<Object...>})</lang>
D
Standard Doubly-linked List
<lang d>void main() {
import std.stdio, std.container, std.range;
auto dll = DList!dchar("DCBA"d.dup);
dll[].writeln; dll[].retro.writeln;
}</lang>
- Output:
ABCD DCBA
User-defined Doubly-linked list
Same output. <lang d>struct Node(T) {
T data; typeof(this)* prev, next;
}
void prepend(T)(ref Node!T* head, in T item) pure nothrow {
auto newNode = new Node!T(item, null, head);
if (head)
head.prev = newNode;
head = newNode;
}
void main() {
import std.stdio;
Node!char* head;
foreach (char c; "DCBA")
head.prepend(c);
auto last = head;
for (auto p = head; p; p = p.next) {
p.data.write;
last = p;
}
writeln;
for (auto p = last; p; p = p.prev)
p.data.write;
writeln;
}</lang>
Delphi
<lang delphi>uses system ;
type
// declare the list pointer type plist = ^List ;
// declare the list type, a generic data pointer prev and next pointers
List = record
data : pointer ;
prev : pList ;
next : pList ;
end;
// since this task is just showing the traversal I am not allocating the memory and setting up the root node etc. // Note the use of the carat symbol for de-referencing the pointer.
begin
// beginning to end while not (pList^.Next = NIL) do pList := pList^.Next ;
// end to beginning while not (pList^.prev = NIL) do pList := pList^.prev ;
end;</lang>
E
Given the definition in Doubly-linked list/Definition#E, <lang e>def traverse(list) {
var node := list.atFirst()
while (true) {
println(node[])
if (node.hasNext()) {
node := node.next()
} else {
break
}
}
while (true) {
println(node[])
if (node.hasPrev()) {
node := node.prev()
} else {
break
}
}
}</lang>
<lang e>? def list := makeDLList()
- value: <>
? list.push(1) ? list.push(2) ? list.push(3)
? traverse(list) 1 2 3 3 2 1</lang>
Erlang
The task in Doubly-linked_list/Element_insertion uses traversal as proof that the insertion worked.
F#
<lang fsharp> open System.Collections.Generic
let first (l: LinkedList<char>) = l.First let last (l: LinkedList<char>) = l.Last
let next (l: LinkedListNode<char>) = l.Next let prev (l: LinkedListNode<char>) = l.Previous
let traverse g f (ls: LinkedList<char>) =
let rec traverse (l: LinkedListNode<char>) =
match l with
| null -> ()
| _ ->
printf "%A" l.Value
traverse (f l)
traverse (g ls)
let traverseForward = traverse first next let traverseBackward = traverse last prev
let cs = LinkedList(['a'..'z'])
traverseForward cs printfn "" traverseBackward cs </lang>
- Output:
'a''b''c''d''e''f''g''h''i''j''k''l''m''n''o''p''q''r''s''t''u''v''w''x''y''z' 'z''y''x''w''v''u''t''s''r''q''p''o''n''m''l''k''j''i''h''g''f''e''d''c''b''a'
Fortran
Go
Code is identical to that for task Doubly-linked list/Element insertion except for addition of section at the end of main noted "traverse from end to beginning." Traversal from beginning to end is adequately demonstrated by the String method of dlList.
Also note that there is a doubly linked list in the Go standard library in package container/list. <lang go>package main
import "fmt"
type dlNode struct {
string next, prev *dlNode
}
type dlList struct {
head, tail *dlNode
}
func (list *dlList) String() string {
if list.head == nil {
return fmt.Sprint(list.head)
}
r := "[" + list.head.string
for p := list.head.next; p != nil; p = p.next {
r += " " + p.string
}
return r + "]"
}
func (list *dlList) insertTail(node *dlNode) {
if list.tail == nil {
list.head = node
} else {
list.tail.next = node
}
node.next = nil
node.prev = list.tail
list.tail = node
}
func (list *dlList) insertAfter(existing, insert *dlNode) {
insert.prev = existing
insert.next = existing.next
existing.next.prev = insert
existing.next = insert
if existing == list.tail {
list.tail = insert
}
}
func main() {
dll := &dlList{}
fmt.Println(dll)
a := &dlNode{string: "A"}
dll.insertTail(a)
dll.insertTail(&dlNode{string: "B"})
fmt.Println(dll)
dll.insertAfter(a, &dlNode{string: "C"})
fmt.Println(dll)
// traverse from end to beginning
fmt.Print("From tail:")
for p := dll.tail; p != nil; p = p.prev {
fmt.Print(" ", p.string)
}
fmt.Println("")
}</lang> Output:
<nil> [A B] [A C B] From tail: B C A
Haskell
<lang haskell>main = print . traverse True $ create [10,20,30,40]
data DList a = Leaf | Node { prev::(DList a), elt::a, next::(DList a) }
create = go Leaf
where go _ [] = Leaf
go prev (x:xs) = current
where current = Node prev x next
next = go current xs
isLeaf Leaf = True isLeaf _ = False
lastNode Leaf = Leaf lastNode dl = until (isLeaf.next) next dl
traverse _ Leaf = [] traverse True (Node l v Leaf) = v : v : traverse False l traverse dir (Node l v r) = v : traverse dir (if dir then r else l)</lang>
Icon and Unicon
Uses Unicon classes. <lang Unicon>class DoubleLink (value, prev_link, next_link)
# insert given node after this one, removing its existing connections method insert_after (node) node.prev_link := self if (\next_link) then next_link.prev_link := node node.next_link := next_link self.next_link := node end
# use a generator to traverse
# - keep suspending the prev/next link until a null node is reached
method traverse_backwards ()
current := self
while \current do {
suspend current
current := current.prev_link
}
end
method traverse_forwards ()
current := self
while \current do {
suspend current
current := current.next_link
}
end
initially (value, prev_link, next_link) self.value := value self.prev_link := prev_link # links are 'null' if not given self.next_link := next_link
end
procedure main ()
l1 := DoubleLink (1) l2 := DoubleLink (2) l1.insert_after (l2) l1.insert_after (DoubleLink (3))
write ("Traverse from beginning to end")
every (node := l1.traverse_forwards ()) do
write (node.value)
write ("Traverse from end to beginning")
every (node := l2.traverse_backwards ()) do
write (node.value)
end</lang>
Output:
Traverse from beginning to end 1 3 2 Traverse from end to beginning 2 3 1
J
<lang j>traverse=:1 :0
work=. result=. conew 'DoublyLinkedListHead' current=. y while. y ~: current=. successor__current do. work=. (work;result;<u data__current) conew 'DoublyLinkedListElement' end. result
)</lang>
This traverses a doubly linked list, applying the verb u to the data in each list element and creates a new doubly linked list containing the results. A reference to the new doubly linked list is returned.
Java
<lang java> package com.rosettacode;
import java.util.LinkedList; import java.util.stream.Collectors; import java.util.stream.IntStream;
public class DoubleLinkedListTraversing {
public static void main(String[] args) {
final LinkedList<String> doubleLinkedList =
IntStream.range(1, 10)
.mapToObj(String::valueOf)
.collect(Collectors.toCollection(LinkedList::new));
doubleLinkedList.iterator().forEachRemaining(System.out::print); System.out.println(); doubleLinkedList.descendingIterator().forEachRemaining(System.out::print); }
}</lang>
- Output:
123456789 987654321
JavaScript
See Doubly-Linked List (element)#JavaScript. The traverse() and print() functions have been inherited from Singly-Linked List (traversal)#JavaScript.
<lang javascript>DoublyLinkedList.prototype.getTail = function() {
var tail;
this.traverse(function(node){tail = node;});
return tail;
} DoublyLinkedList.prototype.traverseBackward = function(func) {
func(this);
if (this.prev() != null)
this.prev().traverseBackward(func);
} DoublyLinkedList.prototype.printBackward = function() {
this.traverseBackward( function(node) {print(node.value())} );
}
var head = createDoublyLinkedListFromArray([10,20,30,40]); head.print(); head.getTail().printBackward();</lang>
outputs:
10 20 30 40 40 30 20 10
Uses the print() function from Rhino or SpiderMonkey.
Julia
<lang julia>mutable struct DLNode{T}
value::T
pred::Union{DLNode{T}, Nothing}
succ::Union{DLNode{T}, Nothing}
DLNode(v) = new{typeof(v)}(v, nothing, nothing)
end
function insertpost(prevnode, node)
succ = prevnode.succ
prevnode.succ = node
node.pred = prevnode
node.succ = succ
if succ != nothing
succ.pred = node
end
node
end
first(nd) = (while nd.pred != nothing nd = nd.prev end; nd) last(nd) = (while nd.succ != nothing nd = nd.succ end; nd)
function printconnected(nd; fromtail = false)
if fromtail
nd = last(nd)
print(nd.value)
while nd.pred != nothing
nd = nd.pred
print(" -> $(nd.value)")
end
else
nd = first(nd)
print(nd.value)
while nd.succ != nothing
nd = nd.succ
print(" -> $(nd.value)")
end
end
println()
end
node1 = DLNode(1) node2 = DLNode(2) node3 = DLNode(3) insertpost(node1, node2) insertpost(node2, node3) print("From beginning to end: "); printconnected(node1) print("From end to beginning: "); printconnected(node1, fromtail = true)
</lang>
- Output:
From beginning to end: 1 -> 2 -> 3 From end to beginning: 3 -> 2 -> 1
Kotlin
To complete this task, we just need to add a couple of traversal functions to the class we defined in the Doubly-linked list/Definition task: <lang scala>// version 1.1.2
class LinkedList<E> {
class Node<E>(var data: E, var prev: Node<E>? = null, var next: Node<E>? = null) {
override fun toString(): String {
val sb = StringBuilder(this.data.toString())
var node = this.next
while (node != null) {
sb.append(" -> ", node.data.toString())
node = node.next
}
return sb.toString()
}
}
var first: Node<E>? = null var last: Node<E>? = null
fun addFirst(value: E) {
if (first == null) {
first = Node(value)
last = first
}
else {
val node = first!!
first = Node(value, null, node)
node.prev = first
}
}
fun addLast(value: E) {
if (last == null) {
last = Node(value)
first = last
}
else {
val node = last!!
last = Node(value, node, null)
node.next = last
}
}
fun insert(after: Node<E>?, value: E) {
if (after == null)
addFirst(value)
else if (after == last)
addLast(value)
else {
val next = after.next
val new = Node(value, after, next)
after.next = new
if (next != null) next.prev = new
}
}
override fun toString() = first.toString()
fun firstToLast() = first?.toString() ?: ""
fun lastToFirst(): String {
if (last == null) return ""
val sb = StringBuilder(last.toString())
var node = last!!.prev
while (node != null) {
sb.append(" -> ", node.data.toString())
node = node.prev
}
return sb.toString()
}
}
fun main(args: Array<String>) {
val ll = LinkedList<Int>()
ll.addFirst(1)
ll.addLast(4)
ll.insert(ll.first, 2)
ll.insert(ll.last!!.prev, 3)
println("First to last : ${ll.firstToLast()}")
println("Last to first : ${ll.lastToFirst()}")
}</lang>
- Output:
First to last : 1 -> 2 -> 3 -> 4 Last to first : 4 -> 3 -> 2 -> 1
Liberty BASIC
<lang lb> struct block,nxt as ulong,prev as ulong,nm as char[20],age as long'Our structure of the blocks in our list.
global hHeap global hFirst global hLast global blockCount global blockSize blockSize=len(block.struct)
call Init
if hHeap=0 then
print "Error occured! Could not create heap, exiting..."
end
end if
FirstUser=New("David",20)
notImportant=New("Jessica",35)
notImportant=New("Joey",38)
MiddleUser=New("Jack",56)
notImportant=New("Amy",17)
notImportant=New("Bob",28)
LastUser=New("Kenny",56)
print "-Traversing the list forwards"
hCurrent=hFirst
while hCurrent<>0
print tab(2);dechex$(hCurrent);" ";Block.name$(hCurrent);" ";Block.age(hCurrent)
hCurrent=Block.next(hCurrent)
wend
print print "-Deleting first, middle, and last person."
call Delete FirstUser'1 call Delete MiddleUser'2 call Delete LastUser'3
print
print "-Traversing the list backwards"
hCurrent=hLast
while hCurrent<>0
print tab(2);dechex$(hCurrent);" ";Block.name$(hCurrent);" ";Block.age(hCurrent)
hCurrent=Block.prev(hCurrent)
wend
call Uninit
end
function Block.next(hBlock)
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void Block.next=block.nxt.struct
end function
function Block.prev(hBlock)
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void Block.prev=block.prev.struct
end function
function Block.age(hBlock)
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void Block.age=block.age.struct
end function
function Block.name$(hBlock)
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void Block.name$=block.nm.struct
end function
sub Block.age hBlock,age
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void block.age.struct=age calldll #kernel32,"RtlMoveMemory",hBlock as ulong,block as struct,blockSize as long,ret as void
end sub
sub Block.name hBlock,name$
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void block.nm.struct=name$ calldll #kernel32,"RtlMoveMemory",hBlock as ulong,block as struct,blockSize as long,ret as void
end sub
sub Block.next hBlock,nxt
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void block.nxt.struct=nxt calldll #kernel32,"RtlMoveMemory",hBlock as ulong,block as struct,blockSize as long,ret as void
end sub
sub Block.prev hBlock,prev
calldll #kernel32,"RtlMoveMemory",block as struct,hBlock as ulong,blockSize as long,ret as void block.prev.struct=prev calldll #kernel32,"RtlMoveMemory",hBlock as ulong,block as struct,blockSize as long,ret as void
end sub
function New(name$,age)
calldll #kernel32,"HeapAlloc",hHeap as ulong,_HEAP_ZERO_MEMORY as ulong,blockSize as long,New as ulong
if New<>0 then
blockCount=blockCount+1
if hFirst=0 then
hFirst=New
hLast=New
else
call Block.next hLast,New
call Block.prev New,hLast
hLast=New
end if
call Block.name New,name$
call Block.age New,age
end if
end function
sub Delete hBlock
if hBlock<>0 then
blockCount=blockCount-1
if blockCount=0 then
hFirst=0
hLast=0
else
if hBlock=hFirst then
hFirst=Block.next(hBlock)
call Block.prev hFirst,0
else
if hBlock=hLast then
hLast=Block.prev(hBlock)
call Block.next hLast,0
else
call Block.next Block.prev(hBlock),Block.next(hBlock)
call Block.prev Block.next(hBlock),Block.prev(hBlock)
end if
end if
end if
calldll #kernel32,"HeapFree",hHeap as ulong,0 as long,hBlock as ulong,ret as void
end if
end sub
sub Init
calldll #kernel32,"HeapCreate",0 as long,10000 as long,0 as long,hHeap as ulong
end sub
sub Uninit
calldll #kernel32,"HeapDestroy",hHeap as ulong,ret as void
end sub </lang>
Nim
<lang nim>type
List[T] = object head, tail: Node[T]
Node[T] = ref TNode[T]
TNode[T] = object next, prev: Node[T] data: T
proc initList[T](): List[T] = discard
proc newNode[T](data: T): Node[T] =
new(result) result.data = data
proc prepend[T](l: var List[T], n: Node[T]) =
n.next = l.head if l.head != nil: l.head.prev = n l.head = n if l.tail == nil: l.tail = n
proc append[T](l: var List[T], n: Node[T]) =
n.next = nil n.prev = l.tail if l.tail != nil: l.tail.next = n l.tail = n if l.head == nil: l.head = n
proc insertAfter[T](l: var List[T], r, n: Node[T]) =
n.prev = r n.next = r.next n.next.prev = n r.next = n if r == l.tail: l.tail = n
proc remove[T](l: var List[T], n: Node[T]) =
if n == l.tail: l.tail = n.prev if n == l.head: l.head = n.next if n.next != nil: n.next.prev = n.prev if n.prev != nil: n.prev.next = n.next
proc `$`[T](l: var List[T]): string =
result = ""
var n = l.head
while n != nil:
if result.len > 0: result.add(" -> ")
result.add($n.data)
n = n.next
iterator traverseForward[T](l: List[T]): T =
var n = l.head while n != nil: yield n.data n = n.next
iterator traverseBackward[T](l: List[T]): T =
var n = l.tail while n != nil: yield n.data n = n.prev
var l = initList[int]() var n = newNode(12) var m = newNode(13) var i = newNode(14) var j = newNode(15) l.append(n) l.prepend(m) l.insertAfter(m, i) l.prepend(j) l.remove(m)
for i in l.traverseForward():
echo "> ", i
for i in l.traverseBackward():
echo "< ", i</lang>
Oberon-2
<lang oberon2> MODULE Collections; IMPORT Box;
TYPE
Action = PROCEDURE (o: Box.Object);
PROCEDURE (dll: DLList) GoForth*(do: Action);
VAR iter: Node; BEGIN iter := dll.first; WHILE iter # NIL DO do(iter.value); iter := iter.next END END GoForth;
PROCEDURE (dll: DLList) GoBack*(do: Action); VAR iter: Node; BEGIN ASSERT(dll.last # NIL); iter := dll.last; WHILE iter # NIL DO do(iter.value); iter := iter.prev END END GoBack;
END Collections. </lang>
Objeck
<lang objeck> class Traverse {
function : Main(args : String[]) ~ Nil {
list := Collection.IntList->New();
list->Insert(100);
list->Insert(50);
list->Insert(25);
list->Insert(10);
list->Insert(5);
"-- forward --"->PrintLine();
list->Rewind();
while(list->More()) {
list->Get()->PrintLine();
list->Next();
};
"-- backward --"->PrintLine();
list->Forward();
while(list->More()) {
list->Get()->PrintLine();
list->Previous();
};
}
} </lang>
-- forward -- 100 5 10 25 50 -- backward -- 50 25 10 5 100
Oforth
Complete definition is here : Doubly-linked list/Definition#Oforth
Defining #forEachNext and #forEachPrev allow to traverse this double linked list using #forEach: and #revEach: syntax
<lang oforth>DList method: forEachNext
dup ifNull: [ drop @head ifNull: [ false ] else: [ @head @head true] return ] next dup ifNull: [ drop false ] else: [ dup true ] ;
DList method: forEachPrev
dup ifNull: [ drop @tail ifNull: [ false ] else: [ @tail @tail true] return ] prev dup ifNull: [ drop false ] else: [ dup true ] ;
- test
| dl n |
DList new ->dl
dl insertFront("A")
dl insertBack("B")
dl head insertAfter(DNode new("C", null , null))
"Traversal (beginning to end) : " println dl forEach: n [ n . ]
"\nTraversal (end to beginning) : " println dl revEach: n [ n . ] ;</lang>
- Output:
>test Traversal (beginning to end) : A C B Traversal (end to beginning) : B C A ok
Oz
Warning: Highly unidiomatic code. (Use built-in lists instead.) <lang oz>declare
proc {Walk Node Action}
case Node of nil then skip
[] node(value:V next:N ...) then
{Action V} {Walk @N Action}
end end
proc {WalkBackwards Node Action}
Tail = {GetLast Node}
proc {Loop N}
case N of nil then skip [] node(value:V prev:P ...) then {Action V} {Loop @P} end
end
in
{Loop Tail}
end
fun {GetLast Node}
case @(Node.next) of nil then Node
[] NextNode=node(...) then {GetLast NextNode}
end
end
fun {CreateNewNode Value}
node(prev:{NewCell nil}
next:{NewCell nil}
value:Value)
end
proc {InsertAfter Node NewNode}
Next = Node.next
in
(NewNode.next) := @Next
(NewNode.prev) := Node
case @Next of nil then skip
[] node(prev:NextPrev ...) then
NextPrev := NewNode
end
Next := NewNode
end
A = {CreateNewNode a}
B = {CreateNewNode b}
C = {CreateNewNode c}
in
{InsertAfter A B}
{InsertAfter A C}
{Walk A Show}
{WalkBackwards A Show}</lang>
Pascal
See Delphi
Phix
<lang Phix>enum NEXT,PREV,DATA constant empty_dll = Template:1,1 sequence dll = empty_dll
procedure insert_after(object data, integer pos=1) integer prv = dll[pos][PREV]
dll = append(dll,{pos,prv,data})
if prv!=0 then
dll[prv][NEXT] = length(dll)
end if
dll[pos][PREV] = length(dll)
end procedure
insert_after("ONE") insert_after("TWO") insert_after("THREE")
?dll
procedure show(integer d) integer idx = dll[1][d]
while idx!=1 do
?dll[idx][DATA]
idx = dll[idx][d]
end while
end procedure show(NEXT) ?"==" show(PREV)</lang>
- Output:
{{2,4},{3,1,"ONE"},{4,2,"TWO"},{1,3,"THREE"}}
"ONE"
"TWO"
"THREE"
"=="
"THREE"
"TWO"
"ONE"
PicoLisp
<lang PicoLisp># Print the elements a doubly-linked list (de 2print (DLst)
(for (L (car DLst) L (cddr L))
(printsp (car L)) )
(prinl) )
- Print the elements a doubly-linked list in reverse order
(de 2printReversed (DLst)
(for (L (cdr DLst) L (cadr L))
(printsp (car L)) )
(prinl) )</lang>
Output for the example data produced in Doubly-linked list/Definition#PicoLisp and Doubly-linked list/Element definition#PicoLisp:
: (2print *DLst) # Print the list not was it a cat I saw : (2printReversed *DLst) # Print it in reversed order saw I cat a it was not
Output for the example data produced in Doubly-linked list/Element insertion#PicoLisp:
: (2print *DL) # Print the list A C B : (2printReversed *DL) # Print it in reversed order B C A
PL/I
<lang PL/I>/* To implement a doubly-linked list -- i.e., a 2-way linked list. */ doubly_linked_list: proc options (main);
define structure
1 node,
2 value fixed,
2 fwd_pointer handle(node),
2 back_pointer handle(node);
declare (head, tail, t) handle (node); declare null builtin; declare i fixed binary;
head, tail = bind(:node, null:);
do i = 1 to 10; /* Add ten items to the tail of the queue. */
if head = bind(:node, null:) then
do;
head,tail = new(:node:);
get list (head => value);
put skip list (head => value);
head => back_pointer,
head => fwd_pointer = bind(:node, null:); /* A NULL link */
end;
else
do;
t = new(:node:);
t => back_pointer = tail; /* Point the new tail back to the old */
/* tail. */
tail => fwd_pointer = t; /* Point the tail to the new node. */
t => back_pointer = tail; /* Point the new tail back to the old */
/* tail. */
tail = t; /* Point at the new tail. */
tail => fwd_pointer = bind(:node, null:);
/* Set the tail link to NULL */
get list (tail => value) copy;
put skip list (tail => value);
end;
end;
if head = bind(:node, null:) then return; /* Empty list. */
/* Traverse the list from the head. */
put skip list ('In a forwards direction, the list has:');
t = head;
do while (t ^= bind(:node, null:));
put skip list (t => value);
t = t => fwd_pointer;
end;
/* Traverse the list from the tail to the head. */
put skip list ('In the reverse direction, the list has:');
t = tail;
do while (t ^= bind(:node, null:));
put skip list (t => value);
t = t => back_pointer;
end;
end doubly_linked_list;</lang> Output:
In a forwards direction, the list has:
1
2
3
4
5
16
7
8
9
10
In the reverse direction, the list has:
10
9
8
7
16
5
4
3
2
1
PureBasic
<lang PureBasic>NewList MyData.i() ; Create a double linked list holding a single value (integer)
- Set up a randomly long linked list in the range 25-125 elements
For i=0 To (Random(100)+25)
AddElement(MyData()) ; Create a new tailing element MyData()=Random(314) ; Inert a vale into it
Next
- Traverse from the beginning of a doubly-linked list to the end.
FirstElement(MyData()) Repeat
Debug MyData() ; Present the value in the current cell
Until Not NextElement(MyData())
- Traverse from the end to the beginning.
LastElement(MyData()) Repeat
Debug MyData() ; Present the value in the current cell
Until Not PreviousElement(MyData())</lang>
Python
This provides two solutions. One that explicitly builds a linked list and traverses it two ways, and another which uses pythons combined list/array class. Unless two lists explicitly needed to be spliced together in O(1) time, or a double linked list was needed for some other reason, most python programmers would probably use the second solution. <lang python>class List:
def __init__(self, data, next=None, prev=None):
self.data = data
self.next = next
self.prev = prev
def append(self, data):
if self.next == None:
self.next = List(data, None, self)
return self.next
else:
return self.next.append(data)
- Build the list
tail = head = List(10) for i in [ 20, 30, 40 ]:
tail = tail.append(i)
- Traverse forwards
node = head while node != None:
print(node.data) node = node.next
- Traverse Backwards
node = tail while node != None:
print(node.data) node = node.prev</lang>
This produces the desired output. However, I expect most python programmers would do the following instead:
<lang python>l = [ 10, 20, 30, 40 ] for i in l:
print(i)
for i in reversed(l): # reversed produces an iterator, so only O(1) memory is used
print(i)</lang>
Double-ended queues in python are provided by the collections.deque class and the array/list type can perform all the operations of a C++ vector (and more), so building one's own doubly-linked list would be restricted to very specialized situations.
Racket
See Doubly-Linked List for the structure definitions.
These functions traverse the list in the two directions. They create a native (singly-linked) list by adding to the front, so they traverse in the reverse order from the desired result order. <lang racket>(define (dlist-elements dlist)
(let loop ([elements '()] [dlink (dlist-tail dlist)])
(if dlink
(loop (cons (dlink-content dlink) elements) (dlink-prev dlink))
elements)))
(define (dlist-elements/reverse dlist)
(let loop ([elements '()] [dlink (dlist-head dlist)])
(if dlink
(loop (cons (dlink-content dlink) elements) (dlink-next dlink))
elements)))</lang>
Raku
(formerly Perl 6) Since the list routines are supplied by the generic roles defined in Doubly-linked_list/Definition#Perl_6, it suffices to say: <lang perl6>say $dll.list; say $dll.reverse;</lang> These automatically return just the payloads, hiding the elements containing the forward and backward pointers.
REXX
REXX doesn't have linked lists, as there are no pointers (or handles). However, linked lists can be simulated with lists in REXX. <lang rexx>/*REXX program that implements various List Manager functions. */ /*┌────────────────────────────────────────────────────────────────────┐ ┌─┘ Functions of the List Manager └─┐ │ │ │ @init ─── initializes the List. │ │ │ │ @size ─── returns the size of the List [could be 0 (zero)]. │ │ │ │ @show ─── shows (displays) the complete List. │ │ @show k,1 ─── shows (displays) the Kth item. │ │ @show k,m ─── shows (displays) M items, starting with Kth item. │ │ @show ,,─1 ─── shows (displays) the complete List backwards. │ │ │ │ @get k ─── returns the Kth item. │ │ @get k,m ─── returns the M items starting with the Kth item. │ │ │ │ @put x ─── adds the X items to the end (tail) of the List. │ │ @put x,0 ─── adds the X items to the start (head) of the List. │ │ @put x,k ─── adds the X items to before of the Kth item. │ │ │ │ @del k ─── deletes the item K. │ │ @del k,m ─── deletes the M items starting with item K. │ └─┐ ┌─┘
└────────────────────────────────────────────────────────────────────┘*/
call sy 'initializing the list.' ; call @init call sy 'building list: Was it a cat I saw'; call @put 'Was it a cat I saw' call sy 'displaying list size.' ; say 'list size='@size() call sy 'forward list' ; call @show call sy 'backward list' ; call @show ,,-1 call sy 'showing 4th item' ; call @show 4,1 call sy 'showing 6th & 6th items' ; call @show 5,2 call sy 'adding item before item 4: black' ; call @put 'black',4 call sy 'showing list' ; call @show call sy 'adding to tail: there, in the ...'; call @put 'there, in the shadows, stalking its prey (and next meal).' call sy 'showing list' ; call @show call sy 'adding to head: Oy!' ; call @put 'Oy!',0 call sy 'showing list' ; call @show exit /*stick a fork in it, we're done.*/ /*──────────────────────────────────subroutines─────────────────────────*/ p: return word(arg(1),1) sy: say; say left(,30) "───" arg(1) '───'; return @hasopt: arg o; return pos(o,opt)\==0 @size: return $.# @init: $.@=; $.#=0; return 0 @adjust: $.@=space($.@); $.#=words($.@); return 0
@parms: arg opt
if @hasopt('k') then k=min($.#+1,max(1,p(k 1)))
if @hasopt('m') then m=p(m 1)
if @hasopt('d') then dir=p(dir 1)
return
@show: procedure expose $.; parse arg k,m,dir
if dir==-1 & k== then k=$.#
m=p(m $.#);
call @parms 'kmd'
say @get(k,m,dir);
return 0
@get: procedure expose $.; arg k,m,dir,_
call @parms 'kmd'
do j=k for m by dir while j>0 & j<=$.#
_=_ subword($.@,j,1)
end /*j*/
return strip(_)
@put: procedure expose $.; parse arg x,k
k=p(k $.#+1)
call @parms 'k'
$.@=subword($.@,1,max(0,k-1)) x subword($.@,k)
call @adjust
return 0
@del: procedure expose $.; arg k,m
call @parms 'km'
_=subword($.@,k,k-1) subword($.@,k+m)
$.@=_
call @adjust
return</lang>
output
─── initializing the list. ───
─── building list: Was it a cat I saw ───
─── displaying list size. ───
list size=6
─── forward list ───
Was it a cat I saw
─── backward list ───
saw I cat a it Was
─── showing 4th item ───
cat
─── showing 6th & 6th items ───
I saw
─── adding item before item 4: black ───
─── showing list ───
Was it a black cat I saw
─── adding to tail: there, in the ... ───
─── showing list ───
Was it a black cat I saw there, in the shadows, stalking its prey (and next meal
─── adding to head: Oy! ───
─── showing list ───
Oy! Was it a black cat I saw there, in the shadows, stalking its prey (and next
Ring
<lang ring>
- Project : Doubly-linked list/Traversal
trav = [123, 789, 456] travfor = sort(trav) see "Traverse forwards:" + nl see travfor see nl travback = reverse(travfor) see "Traverse backwards:" + nl see travback see nl </lang> Output:
Traverse forwards: 123 456 789 Traverse backwards: 789 456 123
Ruby
<lang ruby>class DListNode
def get_tail
# parent class (ListNode) includes Enumerable, so the find method is available to us
self.find {|node| node.succ.nil?}
end
def each_previous(&b) yield self self.prev.each_previous(&b) if self.prev end
end
head = DListNode.from_array([:a, :b, :c]) head.each {|node| p node.value} head.get_tail.each_previous {|node| p node.value}</lang>
Salmon
Without explicit type information: <lang Salmon>class item(init_data)
{
variable next,
previous,
data := init_data;
};
function prepend(tail, new_data)
{
immutable result := item(new_data);
result.next := tail;
result.previous := null;
if (tail != null)
tail.previous := result;;
return result;
};
variable my_list := null; my_list := prepend(my_list, "R"); my_list := prepend(my_list, "o"); my_list := prepend(my_list, "s"); my_list := prepend(my_list, "e"); my_list := prepend(my_list, "t"); my_list := prepend(my_list, "t"); my_list := prepend(my_list, "a");
"Items in the list going forward:"! variable follow := my_list; while (true)
{
follow.data!
if (follow.next == null)
break;;
}
step
follow := follow.next;;
"Items in the list going backward:"! while (follow != null)
follow.data!
step
follow := follow.previous;;</lang>
With explicit type information: <lang Salmon>class item(init_data : string)
{
variable next: item | {null},
previous : item | {null},
data : string := init_data;
};
function prepend(tail : item | {null}, new_data : string) returns item
{
immutable result := item(new_data);
result.next := tail;
result.previous := null;
if (tail != null)
tail.previous := result;;
return result;
};
variable my_list : item | {null} := null; my_list := prepend(my_list, "R"); my_list := prepend(my_list, "o"); my_list := prepend(my_list, "s"); my_list := prepend(my_list, "e"); my_list := prepend(my_list, "t"); my_list := prepend(my_list, "t"); my_list := prepend(my_list, "a");
"Items in the list going forward:"! variable follow : item | {null} := my_list; while (true)
{
follow.data!
if (follow.next == null)
break;;
}
step
follow := follow.next;;
"Items in the list going backward:"! while (follow != null)
follow.data!
step
follow := follow.previous;;</lang>
Both of these produce the following output:
Items in the list going forward: a t t e s o R Items in the list going backward: R o s e t t a
Scala
<lang Scala>import java.util
object DoublyLinkedListTraversal extends App {
private val ll = new util.LinkedList[String]
private def traverse(iter: util.Iterator[String]) = while (iter.hasNext) iter.next
traverse(ll.iterator) traverse(ll.descendingIterator)
}</lang>
Tcl
Assuming that the List class from this other task is already present...
<lang tcl># Modify the List class to add the iterator methods
oo::define List {
method foreach {varName script} {
upvar 1 $varName v
for {set node [self]} {$node ne ""} {set node [$node next]} {
set v [$node value]
uplevel 1 $script
}
}
method revforeach {varName script} {
upvar 1 $varName v
for {set node [self]} {$node ne ""} {set node [$node previous]} {
set v [$node value]
uplevel 1 $script
}
}
}
- Demonstrating...
set first [List new a [List new b [List new c [set last [List new d]]]]] puts "Forward..." $first foreach char { puts $char } puts "Backward..." $last revforeach char { puts $char }</lang> Which produces this output:
Forward... a b c d Backward... d c b a
zkl
<lang zkl>class Node{
fcn init(_value,_prev=Void,_next=Void)
{ var value=_value, prev=_prev, next=_next; }
fcn toString{ value.toString() }
fcn append(value){
b,c := Node(value,self,next),next;
next=b;
if(c) c.prev=b;
b
}
}</lang> <lang zkl>a,c := Node("a"), a.append("b").append("c"); n:=a; while(n){ print(n," "); n=n.next } println(); n:=c; while(n){ print(n," "); n=n.prev } println();</lang>
- Output:
a b c c b a