Singly-linked list/Element definition: Difference between revisions
No edit summary |
|||
| Line 884: | Line 884: | ||
end |
end |
||
end</lang> |
end</lang> |
||
This allows us to define an entire list in a single (albeit confusing) line of source. |
|||
<lang nanoquery>linkedlist = new(link, 1, new(link, 2, new(link, 3, new(link, 4, null))))</lang> |
|||
=={{header|Nim}}== |
=={{header|Nim}}== |
||
Revision as of 16:39, 31 January 2020
You are encouraged to solve this task according to the task description, using any language you may know.
Define the data structure for a singly-linked list element. Said element should contain a data member capable of holding a numeric value, and the link to the next element should be mutable.
- 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
360 Assembly
The program uses DSECT and USING pseudo instruction to define a node. <lang 360asm>* Singly-linked list/Element definition 07/02/2017 LISTSINA CSECT
USING LISTSINA,R13 base register
B 72(R15) skip savearea
DC 17F'0' savearea
STM R14,R12,12(R13) prolog
ST R13,4(R15) " <-
ST R15,8(R13) " ->
LR R13,R15 " addressability
- Allocate A
GETMAIN RU,LV=12 get storage
USING NODE,R11 make storage addressable
LR R11,R1 "
MVC VAL,=CL8'A' val='A'
MVC NEXT,=A(0)
DROP R11 base no longer needed
ST R11,A A=@A
- Init LIST
ST R11,LIST init LIST with A
- Allocate C
GETMAIN RU,LV=12 get storage
USING NODE,R11 make storage addressable
LR R11,R1 "
MVC VAL,=CL8'C' val='C'
MVC NEXT,=A(0)
DROP R11 base no longer needed
ST R11,C C=@C
- Insert C After A
MVC P1,A
MVC P2,C
LA R1,PARML
BAL R14,INSERTAF
- Allocate B
GETMAIN RU,LV=12 get storage
USING NODE,R11 make storage addressable
LR R11,R1 "
MVC VAL,=CL8'B' val='B'
MVC NEXT,=A(0)
DROP R11 base no longer needed
ST R11,B B=@B
- Insert B After A
MVC P1,A
MVC P2,B
LA R1,PARML
BAL R14,INSERTAF
- List all
L R11,LIST
USING NODE,R11 address node
LOOP C R11,=A(0)
BE ENDLIST
XPRNT VAL,8
L R11,NEXT
B LOOP
ENDLIST DROP R11
FREEMAIN A=A,LV=12 free A
FREEMAIN A=B,LV=12 free B
FREEMAIN A=C,LV=12 free C
RETURN L R13,4(0,R13) epilog
LM R14,R12,12(R13) " restore
XR R15,R15 " rc=0
BR R14 exit
LIST DS A list head A DS A B DS A C DS A PARML DS 0A P1 DS A P2 DS A INSERTAF CNOP 0,4
L R2,0(R1) @A
L R3,4(R1) @B
USING NODE,R2 ->A
L R4,NEXT @C
DROP R2
USING NODE,R3 ->B
ST R4,NEXT B.NEXT=@C
DROP R3
USING NODE,R2 ->A
ST R3,NEXT A.NEXT=@B
DROP R2
BR R14 return
LTORG all literals
NODE DSECT node (size=12) VAL DS CL8 NEXT DS A
YREGS
END LISTSINA</lang>
- Output:
A B C
AArch64 Assembly
<lang AArch64 Assembly> /* ARM assembly AARCH64 Raspberry PI 3B */ /* program defList.s */
/*******************************************/ /* Constantes file */ /*******************************************/ /* for this file see task include a file in language AArch64 assembly*/ .include "../includeConstantesARM64.inc"
.equ NBELEMENTS, 100 // list size /*******************************************/ /* Structures */ /********************************************/ /* structure linkedlist*/
.struct 0
llist_next: // next element
.struct llist_next + 8
llist_value: // element value
.struct llist_value + 8
llist_fin: /*******************************************/ /* Initialized data */ /*******************************************/ .data szMessInitListe: .asciz "List initialized.\n" szCarriageReturn: .asciz "\n" /* datas error display */ szMessErreur: .asciz "Error detected.\n" /*******************************************/ /* UnInitialized data */ /*******************************************/ .bss lList1: .skip llist_fin * NBELEMENTS // list memory place /*******************************************/ /* code section */ /*******************************************/ .text .global main main:
ldr x0,qAdrlList1 mov x1,#0 str x1,[x0,#llist_next] ldr x0,qAdrszMessInitListe bl affichageMess
100: // standard end of the program
mov x8, #EXIT // request to exit program svc 0 // perform system call
qAdrszMessInitListe: .quad szMessInitListe qAdrszMessErreur: .quad szMessErreur qAdrszCarriageReturn: .quad szCarriageReturn qAdrlList1: .quad lList1 /********************************************************/ /* File Include fonctions */ /********************************************************/ /* for this file see task include a file in language AArch64 assembly */ .include "../includeARM64.inc" </lang>
ACL2
The built in pair type, cons, is sufficient for defining a linked list. ACL2 does not have mutable variables, so functions must instead return a copy of the original list.
<lang Lisp>(let ((elem 8)
(next (list 6 7 5 3 0 9))) (cons elem next))</lang>
Output:
(8 6 7 5 3 0 9)
ActionScript
<lang ActionScript>package { public class Node { public var data:Object = null; public var link:Node = null;
public function Node(obj:Object) { data = obj; } } }</lang>
Ada
<lang ada>type Link; type Link_Access is access Link; type Link is record
Next : Link_Access := null; Data : Integer;
end record;</lang>
ALGOL 68
File: prelude/single_link.a68<lang algol68># -*- coding: utf-8 -*- # CO REQUIRES:
MODE OBJVALUE = ~ # Mode/type of actual obj to be stacked #
END CO
MODE OBJNEXTLINK = STRUCT(
REF OBJNEXTLINK next, OBJVALUE value # ... etc. required #
);
PROC obj nextlink new = REF OBJNEXTLINK:
HEAP OBJNEXTLINK;
PROC obj nextlink free = (REF OBJNEXTLINK free)VOID:
next OF free := obj stack empty # give the garbage collector a BIG hint #</lang>See also: Stack
ALGOL W
<lang algolw> % record type to hold a singly linked list of integers %
record ListI ( integer iValue; reference(ListI) next );
% declare a variable to hold a list % reference(ListI) head;
% create a list of integers % head := ListI( 1701, ListI( 9000, ListI( 42, ListI( 90210, null ) ) ) );</lang>
ARM Assembly
<lang ARM Assembly> /* ARM assembly Raspberry PI */ /* program defList.s */
/* Constantes */ .equ STDOUT, 1 @ Linux output console .equ EXIT, 1 @ Linux syscall .equ READ, 3 .equ WRITE, 4
.equ NBELEMENTS, 100 @ list size
/*******************************************/ /* Structures */ /********************************************/ /* structure linkedlist*/
.struct 0
llist_next: @ next element
.struct llist_next + 4
llist_value: @ element value
.struct llist_value + 4
llist_fin: /* Initialized data */ .data szMessInitListe: .asciz "List initialized.\n" szCarriageReturn: .asciz "\n" /* datas error display */ szMessErreur: .asciz "Error detected.\n"
/* UnInitialized data */ .bss lList1: .skip llist_fin * NBELEMENTS @ list memory place
/* code section */ .text .global main main:
ldr r0,iAdrlList1 mov r1,#0 str r1,[r0,#llist_next] ldr r0,iAdrszMessInitListe 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 iAdrszCarriageReturn: .int szCarriageReturn iAdrlList1: .int lList1 /******************************************************************/ /* display text with size calculation */ /******************************************************************/ /* r0 contains the address of the message */ affichageMess:
push {r0,r1,r2,r7,lr} @ save registers
mov r2,#0 @ counter length */
1: @ loop length calculation
ldrb r1,[r0,r2] @ read octet start position + index
cmp r1,#0 @ if 0 its over
addne r2,r2,#1 @ else add 1 in the length
bne 1b @ and loop
@ so here r2 contains the length of the message
mov r1,r0 @ address message in r1
mov r0,#STDOUT @ code to write to the standard output Linux
mov r7, #WRITE @ code call system "write"
svc #0 @ call system
pop {r0,r1,r2,r7,lr} @ restaur registers
bx lr @ return
</lang>
AutoHotkey
<lang AutoHotkey>element = 5 ; data element_next = element2 ; link to next element</lang>
AWK
Awk only has global associative arrays, which will be used for the list. Numerical indexes into the array will serve as node pointers. A list element will have the next node pointer separated from the value by the pre-defined SUBSEP value. A function will be used to access a node's next node pointer or value given a node pointer (array index). The first array element will serve as the list head.
<lang awk> BEGIN {
NIL = 0 HEAD = 1 LINK = 1 VALUE = 2 delete list initList()
}
function initList() {
delete list list[HEAD] = makeNode(NIL, NIL)
}
function makeNode(link, value) {
return link SUBSEP value
}
function getNode(part, nodePtr, linkAndValue) {
split(list[nodePtr], linkAndValue, SUBSEP) return linkAndValue[part]
} </lang>
Axe
<lang axe>Lbl LINK r₂→{r₁}ʳ 0→{r₁+2}ʳ r₁ Return
Lbl NEXT {r₁+2}ʳ Return
Lbl VALUE {r₁}ʳ Return</lang>
BBC BASIC
<lang bbcbasic> DIM node{pNext%, iData%} </lang>
Bracmat
Data mutation is not Bracmatish, but it can be done. Here is a datastructure for a mutable data value and for a mutable reference. <lang bracmat>link =
(next=) (data=)</lang>
Example of use: <lang bracmat> new$link:?link1 & new$link:?link2 & first thing:?(link1..data) & secundus:?(link2..data) & '$link2:(=?(link1..next)) & !(link1..next..data)</lang> The last line returns
secundus
C
<lang c>struct link {
struct link *next; int data;
};</lang>
C++
The simplest C++ version looks basically like the C version:
<lang cpp>struct link {
link* next; int data;
};</lang>
Initialization of links on the heap can be simplified by adding a constructor:
<lang cpp>struct link {
link* next;
int data;
link(int a_data, link* a_next = 0): next(a_next), data(a_data) {}
};</lang>
With this constructor, new nodes can be initialized directly at allocation; e.g. the following code creates a complete list with just one statement:
<lang cpp> link* small_primes = new link(2, new link(3, new link(5, new link(7))));</lang>
However, C++ also allows to make it generic on the data type (e.g. if you need large numbers, you might want to use a larger type than int, e.g. long on 64-bit platforms, long long on compilers that support it, or even a bigint class).
<lang cpp>template<typename T> struct link {
link* next;
T data;
link(T a_data, link* a_next = 0): next(a_next), data(a_data) {}
};</lang>
Note that the generic version works for any type, not only integral types.
C#
<lang csharp>class LinkedListNode {
public int Value { get; set; }
public LinkedListNode Next { get; set; }
// A constructor is not necessary, but could be useful.
public Link(int value, LinkedListNode next = null)
{
Item = value;
Next = next;
}
}</lang>
A generic version: <lang csharp>class LinkedListNode<T> {
public T Value { get; set; }
public LinkedListNode Next { get; set; }
public Link(T value, LinkedListNode next = null)
{
Item = value;
Next = next;
}
}</lang>
The most C-like possible version is basically C. <lang csharp>unsafe struct link {
public link* next; public int data;
};</lang>
Clojure
As with other LISPs, this is built in. Clojure provides a nice abstraction of lists with its use of: sequences (also called seqs).
<lang clojure>(cons 1 (cons 2 (cons 3 nil))) ; =>(1 2 3)</lang>
Note: this is an immutable data structure. With cons you are constructing a new seq.
Common Lisp
The built-in cons type is used to construct linked lists. Using another type would be unidiomatic and inefficient.
<lang lisp>(cons 1 (cons 2 (cons 3 nil)) => (1 2 3)</lang>
Clean
<lang clean>import StdMaybe
- Link t = { next :: Maybe (Link t), data :: t }</lang>
D
Generic template-based node element.
<lang d>struct SLinkedNode(T) {
T data; typeof(this)* next;
}
void main() {
alias SLinkedNode!int N; N* n = new N(10);
}</lang> Also the Phobos library contains a singly-linked list, std.container.SList. Tango contains tango.util.collection.LinkSeq.
Delphi
A simple one way list. I use a generic pointer for the data that way it can point to any structure, individual variable or whatever. Note that in Standard Pascal, there are no generic pointers, therefore one has to settle for a specific data type there.
<lang delphi>Type
pOneWayList = ^OneWayList;
OneWayList = record
pData : pointer ;
Next : pOneWayList ;
end;</lang>
E
<lang e>interface LinkedList guards LinkedListStamp {} def empty implements LinkedListStamp {
to null() { return true }
} def makeLink(value :int, var next :LinkedList) {
def link implements LinkedListStamp {
to null() { return false }
to value() { return value }
to next() { return next }
to setNext(new) { next := new }
}
return link
}</lang>
Elena
<lang elena>class Link {
prop int Item;
prop Link Next;
constructor(int item, Link next)
{
Item := item;
Next := next
}
}</lang>
Erlang
Lists are builtin, but Erlang is single assignment. Here we need mutable link to next element. Mutable in Erlang usually means a process, so: <lang Erlang> new( Data ) -> erlang:spawn( fun() -> loop( Data, nonext ) end ). </lang> For the whole module see Singly-linked_list/Element_insertion
Factor
<lang>TUPLE: linked-list data next ;
- <linked-list> ( data -- linked-list )
linked-list new swap >>data ;</lang>
Fantom
<lang fantom> class Node {
const Int value // keep value fixed Node? successor // allow successor to change, also, can be 'null', for end of list
new make (Int value, Node? successor := null)
{
this.value = value
this.successor = successor
}
} </lang>
Forth
Idiomatically,
<lang forth>0 value numbers
- push ( n -- )
here swap numbers , , to numbers ;</lang>
NUMBERS is the head of the list, initially nil (= 0); PUSH adds an element to the list; list cells have the structure {Link,Number}. Speaking generally, Number can be anything and list cells can be as long as desired (e.g., {Link,N1,N2} or {Link,Count,"a very long string"}), but the link is always first - or rather, a link always points to the next link, so that NEXT-LIST-CELL is simply fetch (@). Some operations:
<lang forth>: length ( list -- u )
0 swap begin dup while 1 under+ @ repeat drop ;
- head ( list -- x )
cell+ @ ;
- .numbers ( list -- )
begin dup while dup head . @ repeat drop ;</lang>
Higher-order programming, simple continuations, and immediate words can pull out the parallel code of LENGTH and .NUMBERS . Anonymous and dynamically allocated lists are as straightforward.
Fortran
In ISO Fortran 95 or later: <lang fortran>type node
real :: data type( node ), pointer :: next => null()
end type node ! !. . . . ! type( node ) :: head</lang>
Go
<lang go>type Ele struct {
Data interface{}
Next *Ele
}
func (e *Ele) Append(data interface{}) *Ele {
if e.Next == nil {
e.Next = &Ele{data, nil}
} else {
tmp := &Ele{data, e.Next}
e.Next = tmp
}
return e.Next
}
func (e *Ele) String() string {
return fmt.Sprintf("Ele: %v", e.Data)
}</lang>
Groovy
Solution: <lang groovy>class ListNode {
Object payload
ListNode next
String toString() { "${payload} -> ${next}" }
}</lang>
Test: <lang groovy>def n1 = new ListNode(payload:25) n1.next = new ListNode(payload:88)
println n1</lang>
Output:
25 -> 88 -> null
Haskell
This task is not idiomatic for Haskell. Usually, all data in pure functional programming is immutable, and deconstructed through Pattern Matching. The Prelude already contains a parametrically polymorphic list type that can take any data member type, including numeric values. These lists are then used very frequently. Because of this, lists have additional special syntactic sugar.
An equivalent declaration for such a list type without the special syntax would look like this:
<lang haskell> data List a = Nil | Cons a (List a)</lang>
A declaration like the one required in the task, with an integer as element type and a mutable link, would be
<lang haskell> data IntList s = Nil | Cons Integer (STRef s (IntList s))</lang>
but that would be really awkward to use.
Icon and Unicon
The Icon version works in both Icon and Unicon. Unicon also permits a class-based definition.
Icon
<lang Icon> record Node (value, successor) </lang>
Unicon
<lang Unicon> class Node (value, successor)
initially (value, successor) self.value := value self.successor := successor
end </lang>
With either the record or the class definition, new linked lists are easily created and manipulated:
<lang Icon> procedure main ()
n := Node(1, Node (2)) write (n.value) write (n.successor.value)
end </lang>
J
This task is not idomatic in J -- J has lists natively and while using lists to emulate lists is quite possible, it creates additional overhead at every step of the way. (J's native lists are probably best thought of as arrays with values all adjacent to each other, though they also support constant time append.)
However, for illustrative purposes:
<lang J>list=: 0 2$0 list</lang>
This creates and then displays an empty list, with zero elements. The first number in an item is (supposed to be) the index of the next element of the list (_ for the final element of the list). The second number in an item is the numeric value stored in that list item. The list is named and names are mutable in J which means links are mutable.
To create such a list with one element which contains number 42, we can do the following:
<lang J> list=: ,: _ 42
list
_ 42</lang>
Now list contains one item, with index of the next item and value.
Note: this solution exploits the fact that, in this numeric case, data types for index and for node content are the same. If we need to store, for example, strings in the nodes, we should do something different, for example:
<lang J> list=: 0 2$a: NB. creates list with 0 items
list list=: ,: (<_) , <'some text' NB. creates list with 1 item list
+-+---------+ |_|some text| +-+---------+</lang>
Java
The simplest Java version looks basically like the C++ version:
<lang java>class Link {
Link next; int data;
}</lang>
Initialization of links on the heap can be simplified by adding a constructor:
<lang java>class Link {
Link next;
int data;
Link(int a_data, Link a_next) { next = a_next; data = a_data; }
}</lang>
With this constructor, new nodes can be initialized directly at allocation; e.g. the following code creates a complete list with just one statement:
<lang java> Link small_primes = new Link(2, new Link(3, new Link(5, new Link(7, null))));</lang>
However, Java also allows to make it generic on the data type. This will only work on reference types, not primitive types like int or float (wrapper classes like Integer and Float are available).
<lang java>class Link<T> {
Link<T> next;
T data;
Link(T a_data, Link<T> a_next) { next = a_next; data = a_data; }
}</lang>
JavaScript
<lang javascript>function LinkedList(value, next) {
this._value = value; this._next = next;
} LinkedList.prototype.value = function() {
if (arguments.length == 1)
this._value = arguments[0];
else
return this._value;
} LinkedList.prototype.next = function() {
if (arguments.length == 1)
this._next = arguments[0];
else
return this._next;
}
// convenience function to assist the creation of linked lists. function createLinkedListFromArray(ary) {
var head = new LinkedList(ary[0], null);
var prev = head;
for (var i = 1; i < ary.length; i++) {
var node = new LinkedList(ary[i], null);
prev.next(node);
prev = node;
}
return head;
}
var head = createLinkedListFromArray([10,20,30,40]);</lang>
Julia
<lang julia>abstract type AbstractNode{T} end
struct EmptyNode{T} <: AbstractNode{T} end mutable struct Node{T} <: AbstractNode{T}
data::T
next::AbstractNode{T}
end Node{T}(x) where T = Node{T}(x::T, EmptyNode{T}())
mutable struct LinkedList{T}
head::AbstractNode{T}
end LinkedList{T}() where T = LinkedList{T}(EmptyNode{T}()) LinkedList() = LinkedList{Any}()
Base.isempty(ll::LinkedList) = ll.head isa EmptyNode function lastnode(ll::LinkedList)
if isempty(ll) throw(BoundsError()) end
nd = ll.head
while !(nd.next isa EmptyNode)
nd = nd.next
end
return nd
end
function Base.push!(ll::LinkedList{T}, x::T) where T
nd = Node{T}(x)
if isempty(ll)
ll.head = nd
else
tail = lastnode(ll)
tail.next = nd
end
return ll
end function Base.pop!(ll::LinkedList{T}) where T
if isempty(ll)
throw(ArgumentError("list must be non-empty"))
elseif ll.head.next isa EmptyNode
nd = ll.head
ll.head = EmptyNode{T}()
else
nx = ll.head
while !isa(nx.next.next, EmptyNode)
nx = nx.next
end
nd = nx.next
nx.next = EmptyNode{T}()
end
return nd.data
end
lst = LinkedList{Int}() push!(lst, 1) push!(lst, 2) push!(lst, 3) pop!(lst) # 3 pop!(lst) # 2 pop!(lst) # 1</lang>
Kotlin
<lang scala>// version 1.1.2
class Node<T: Number>(var data: T, var next: Node<T>? = 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()
}
}
fun main(args: Array<String>) {
val n = Node(1, Node(2, Node(3))) println(n)
}</lang>
- Output:
1 -> 2 -> 3
Logo
As with other list-based languages, simple lists are represented easily in Logo.
<lang logo>fput item list ; add item to the head of a list
first list ; get the data butfirst list ; get the remainder bf list ; contraction for "butfirst"</lang>
These return modified lists, but you can also destructively modify lists. These are normally not used because you might accidentally create cycles in the list.
<lang logo>.setfirst list value .setbf list remainder</lang>
Mathematica
<lang Mathematica>Append[{}, x] -> {x}</lang>
Modula-2
<lang modula2>TYPE
Link = POINTER TO LinkRcd; LinkRcd = RECORD Next: Link; Data: INTEGER END;</lang>
Modula-3
<lang modula3>TYPE
Link = REF LinkRcd; LinkRcd = RECORD Next: Link; Data: INTEGER END;</lang>
Nanoquery
The simplest version in Nanoquery is similar to the C version: <lang nanoquery>class link
declare data
declare next
end</lang>
Like Java, it is possible to add a constructor that allows us to set the values on initialization. <lang nanoquery>class link
declare data
declare next
def link(data, next)
this.data = data
this.next = next
end
end</lang>
This allows us to define an entire list in a single (albeit confusing) line of source. <lang nanoquery>linkedlist = new(link, 1, new(link, 2, new(link, 3, new(link, 4, null))))</lang>
Nim
<lang nim>type Node[T] = ref object
next: Node[T] data: T
proc newNode[T](data: T): Node[T] =
Node[T](data: data)
var a = newNode 12 var b = newNode 13 var c = newNode 14</lang>
Objective-C
<lang objc>#import <Foundation/Foundation.h>
@interface RCListElement<T> : NSObject {
RCListElement<T> *next; T datum;
} - (RCListElement<T> *)next; - (T)datum; - (RCListElement<T> *)setNext: (RCListElement<T> *)nx; - (void)setDatum: (T)d; @end
@implementation RCListElement - (RCListElement *)next {
return next;
} - (id)datum {
return datum;
} - (RCListElement *)setNext: (RCListElement *)nx {
RCListElement *p = next; next = nx; return p;
} - (void)setDatum: (id)d {
datum = d;
} @end</lang>
OCaml
This task is not idiomatic for OCaml. OCaml already contains a built-in parametrically polymorphic list type that can take any data member type, including numeric values. These lists are then used very frequently. Because of this, lists have additional special syntactic sugar. OCaml's built-in lists, like most functional data structures, are immutable, and are deconstructed through Pattern Matching.
An equivalent declaration for such a list type without the special syntax would look like this:
<lang ocaml> type 'a list = Nil | Cons of 'a * 'a list</lang>
A declaration like the one required in the task, with an integer as element type and a mutable link, would be
<lang ocaml> type int_list = Nil | Cons of int * int_list ref</lang>
but that would be really awkward to use.
Oforth
<lang Oforth>Collection Class new: LinkedList(data, mutable next)</lang>
ooRexx
The simplest ooRexx version is similar in form to the Java or C++ versions: <lang ooRexx> list = .linkedlist~new index = list~insert("abc") -- insert a first item, keeping the index list~insert("def") -- adds to the end list~insert("123", .nil) -- adds to the begining list~insert("456", index) -- inserts between "abc" and "def" list~remove(index) -- removes "abc"
say "Manual list traversal" index = list~first -- demonstrate traversal loop while index \== .nil
say index~value index = index~next
end
say say "Do ... Over traversal" do value over list
say value
end
-- the main list item, holding the anchor to the links.
- class linkedlist
- method init
expose anchor
-- create this as an empty list anchor = .nil
-- return first link element
- method first
expose anchor return anchor
-- return last link element
- method last
expose anchor
current = anchor
loop while current \= .nil
-- found the last one
if current~next == .nil then return current
current = current~next
end
-- empty
return .nil
-- insert a value into the list, using the convention -- followed by the built-in list class. If the index item -- is omitted, add to the end. If the index item is .nil, -- add to the end. Otherwise, just chain to the provided link.
- method insert
expose anchor use arg value
newLink = .link~new(value)
-- adding to the end
if arg() == 1 then do
if anchor == .nil then anchor = newLink
else self~last~insert(newLink)
end
else do
use arg ,index
if index == .nil then do
if anchor \== .nil then newLink~next = anchor
anchor = newLink
end
else index~insert(newLink)
end
-- the link item serves as an "index"
return newLink
-- remove a link from the chain
- method remove
expose anchor
use strict arg index
-- handle the edge case
if index == anchor then anchor = anchor~next
else do
-- no back link, so we need to scan
previous = self~findPrevious(index)
-- invalid index, don't return any item
if previous == .nil then return .nil
previous~next = index~next
end
-- belt-and-braces, remove the link and return the value
index~next = .nil
return index~value
-- private method to find a link predecessor
- method findPrevious private
expose anchor use strict arg index
-- we're our own precessor if this first if index == anchor then return self
current = anchor
loop while current \== .nil
if current~next == index then return current
current = current~next
end
-- not found
return .nil
-- helper method to allow DO ... OVER traversal
- method makearray
expose anchor array = .array~new
current = anchor
loop while current \= .nil
array~append(current~value)
current = current~next
end
return array
- class link
- method init
expose value next -- by default, initialize both data and next to empty. use strict arg value = .nil, next = .nil
-- allow external access to value and next link
- attribute value
- attribute next
- method insert
expose next use strict arg newNode newNode~next = next next = newNode
</lang>
A link element can hold a reference to any ooRexx object.
Pascal
<lang pascal>type
PLink = ^TLink; TLink = record FNext: PLink; FData: integer; end;</lang>
Perl
Just use an array. You can traverse and splice it any way. Linked lists are way too low level.
However, if all you got is an algorithm in a foreign language, you can use references to accomplish the translation. <lang perl>my %node = (
data => 'say what', next => \%foo_node,
); $node{next} = \%bar_node; # mutable</lang>
Perl 6
With Pair
A Pair (constructed with the => operator) can be treated as a cons cell, and thus used to build a linked lists:
<lang perl6>my $elem = 42 => $nextelem;</lang>
However, because this is not the primary purpose of the Pair type, it suffers from the following limitations:
- The naming of Pair's accessor methods is not idiomatic for this use case (
.keyfor the cell's value, and.valuefor the link to the next cell). - A Pair (unlike an Array) does not automatically wrap its keys/values in item containers – so each cell of the list will be immutable once created, making element insertion/deletion impossible (except inserting at the front).
- It provides no built-in convenience methods for iterating/modifying/transforming such a list.
With custom type
For more flexibility, one would create a custom type:
<lang perl6>class Cell {
has $.value is rw; has Cell $.next is rw; # ...convenience methods here...
}
sub cons ($value, $next) { Cell.new(:$value, :$next) }
my $list = cons 10, (cons 20, (cons 30, Nil));</lang>
Phix
In Phix, types are used for validation and debugging rather than specification purposes. For extensive run-time checking you could use something like <lang Phix>enum NEXT,DATA type slnode(object x)
return (sequence(x) and length(x)=DATA and myotherudt(x[DATA]) and integer(x[NEXT])
end type</lang> But more often you would just use the builtin sequences. It is worth noting that while "node lists", such as {{2},{'A',3},{'B',4},{'C',0}} are one way to hold a linked list (with the first element a dummy header), both "parallel/tag lists" such as {{'A','B','C'},{2,3,0}} and "flat lists" such as {'A',3,'B',5,'C',0} are generally more efficient, and the latter is heavily used in the compiler itself (for the ternary lookup tree, intermediate code, and the pre-packed machine code binary).
Memory is automatically reclaimed the moment items are no longer needed.
See also Singly-linked_list/Element_removal#Phix for some working code
PicoLisp
In PicoLisp, the singly-linked list is the most important data structure. Many built-in functions deal with linked lists. A list consists of interconnected "cells". Cells are also called "cons pairs", because they are constructed with the function 'cons'.
Each cell consists of two parts: A CAR and a CDR. Both may contain (i.e. point to) arbitrary data (numbers, symbols, other cells, or even to itself). In the case of a linked list, the CDR points to the rest of the list.
The CAR of a cell can be manipulated with 'set' and the CDR with 'con'.
PL/I
<lang PL/I> declare 1 node based (p),
2 value fixed,
2 link pointer;
</lang>
Pop11
List are built in into Pop11, so normally on would just use them:
<lang pop11>;;; Use shorthand syntax to create list. lvars l1 = [1 2 three 'four'];
- Allocate a single list node, with value field 1 and the link field
- pointing to empty list
lvars l2 = cons(1, []);
- print first element of l1
front(l1) =>
- print the rest of l1
back(l1) =>
- Use index notation to access third element
l1(3) =>
- modify link field of l2 to point to l1
l1 -> back(l2);
- Print l2
l2 =></lang>
If however one wants to definite equivalent user-defined type, one can do this:
<lang pop11>uses objectclass; define :class ListNode;
slot value = []; slot next = [];
enddefine;
- Allocate new node and assign to l1
newListNode() -> l1;
- Print it
l1 =>
- modify value
1 -> value(l1); l1 =>
- Allocate new node with initialized values and assign to link field
- of l1
consListNode(2, []) -> next(l1); l1 =></lang>
PureBasic
<lang PureBasic>Structure MyData
*next.MyData Value.i
EndStructure</lang>
Python
The Node class implements also iteration for more Pythonic iteration over linked lists.
<lang python>class LinkedList(object):
"""USELESS academic/classroom example of a linked list implemented in Python.
Don't ever consider using something this crude! Use the built-in list() type!
"""
class Node(object): def __init__(self, item): self.value = item self.next = None def __init__(self, item=None): if item is not None: self.head = Node(item); self.tail = self.head else: self.head = None; self.tail = None def append(self, item): if not self.head: self.head = Node(item) self.tail = self.head elif self.tail: self.tail.next = Node(item) self.tail = self.tail.next else: self.tail = Node(item) def __iter__(self): cursor = self.head while cursor: yield cursor.value cursor = cursor.next</lang>
Note: As explained in this class' docstring implementing linked lists and nodes in Python is an utterly pointless academic exercise. It may give on the flavor of the elements that would be necessary in some other programming languages (e.g. using Python as "executable psuedo-code"). Adding methods for finding, counting, removing and inserting elements is left as an academic exercise to the reader. For any practical application use the built-in list() or dict() types as appropriate.
Racket
Unlike other Lisp dialects, Racket's cons cells are immutable, so they cannot be used to satisfy this task. However, Racket also includes mutable pairs which are still the same old mutable singly-linked lists.
<lang Racket>
- lang racket
(mcons 1 (mcons 2 (mcons 3 '()))) ; a mutable list </lang>
REXX
The REXX language doesn't have any native linked lists, but they can be created easily.
The values of a REXX linked list can be anything (nulls, character strings, including any type/kind of number, of course).
<lang rexx>/*REXX program demonstrates how to create and show a single-linked list.*/
@.=0 /*define a null linked list. */
call set@ 3 /*linked list: 12 Proth Primes. */
call set@ 5
call set@ 13
call set@ 17
call set@ 41
call set@ 97
call set@ 113
call set@ 193
call set@ 241
call set@ 257
call set@ 353
call set@ 449
w=@.max_width /*use the maximum width of nums. */
call list@ /*list all the elements in list. */
exit /*stick a fork in it, we're done.*/
/*──────────────────────────────────LIST@ subroutine────────────────────*/
list@: say; w=max(7, @.max_width ) /*use the max width of nums or 7.*/
say center('item',6) center('value',w) center('next',6)
say center( ,6,'─') center( ,w,'─') center( ,6,'─')
p=1
do j=1 until p==0 /*show all entries of linked list*/
say right(j,6) right(@.p._value,w) right(@.p._next,6)
p=@.p._next
end /*j*/
return /*──────────────────────────────────SET@ subroutine─────────────────────*/ set@: procedure expose @.; parse arg y /*get element to be added to list*/ _=@._last /*set the previous last element. */ n=_+1 /*bump last ptr in linked list. */ @._._next=n /*set the next pointer value. */ @._last=n /*define next item in linked list*/ @.n._value=y /*set item to the value specified*/ @.n._next=0 /*set the next pointer value. */ @..y=n /*set a locator pointer to self. */ @.max_width=max(@.max_width,length(y)) /*set maximum width of any value.*/ return /*return to invoker of this sub. */</lang> output
item value next
────── ─────── ──────
1 3 2
2 5 3
3 13 4
4 17 5
5 41 6
6 97 7
7 113 8
8 193 9
9 241 10
10 257 11
11 353 12
12 449 0
Ruby
<lang ruby>class ListNode
attr_accessor :value, :succ
def initialize(value, succ=nil) self.value = value self.succ = succ end
def each(&b) yield self succ.each(&b) if succ end
include Enumerable
def self.from_array(ary)
head = self.new(ary[0], nil)
prev = head
ary[1..-1].each do |val|
node = self.new(val, nil)
prev.succ = node
prev = node
end
head
end
end
list = ListNode.from_array([1,2,3,4])</lang>
Rust
Rust's Option<T> type make the definition of a singly-linked list trivial. The use of Box<T> (an owned pointer) is necessary because it has a known size, thus making sure the struct that contains it can have a finite size.
<lang Rust> struct Node<T> {
elem: T, next: Option<Box<Node<T>>>,
}</lang>
However, the above example would not be suitable for a library because, first and foremost, it is private by default but simply making it public would not allow for any encapsulation.
<lang Rust>type Link<T> = Option<Box<Node<T>>>; // Type alias pub struct List<T> { // User-facing interface for list
head: Link<T>,
}
struct Node<T> { // Private implementation of Node
elem: T, next: Link<T>,
}
impl<T> List<T> {
#[inline]
pub fn new() -> Self { // List constructor
List { head: None }
// Add other methods here
}</lang>
Then a separate program could utilize the basic implementation above like so: <lang rust>extern crate LinkedList; // Name is arbitrary here
use LinkedList::List;
fn main() {
let list = List::new(); // Do stuff
}</lang>
Run BASIC
<lang runbasic>data = 10 link = 10 dim node{data,link} </lang>
Scala
Immutable lists that you can use with pattern matching.
<lang scala> sealed trait List[+A] case class Cons[+A](head: A, tail: List[A]) extends List[A] case object Nil extends List[Nothing]
object List {
def apply[A](as: A*): List[A] = if (as.isEmpty) Nil else Cons(as.head, apply(as.tail: _*))
} </lang>
Basic usage
<lang scala> def main(args: Array[String]): Unit = {
val words = List("Rosetta", "Code", "Scala", "Example")
} </lang>
Scheme
Scheme, like other Lisp dialects, has extensive support for singly-linked lists. The element of such a list is known as a cons-pair, because you use the cons function to construct it: <lang scheme>(cons value next)</lang>
The value and next-link parts of the pair can be deconstructed using the car and cdr functions, respectively: <lang scheme>(car my-list) ; returns the first element of the list (cdr my-list) ; returns the remainder of the list</lang>
Each of these parts are mutable and can be set using the set-car! and set-cdr! functions, respectively: <lang scheme>(set-car! my-list new-elem) (set-cdr! my-list new-next)</lang>
Sidef
<lang ruby>var node = Hash.new(
data => 'say what', next => foo_node,
);
node{:next} = bar_node; # mutable</lang>
SSEM
At the machine level, an element of a linked list can be represented using two successive words of storage where the first holds an item of data and the second holds either (a) the address where the next such pair of words will be found, or (b) a special NIL address indicating that we have reached the end of the list. Here is one way in which the list '(1 2 3) could be represented in SSEM code: <lang ssem>01000000000000000000000000000000 26. 2 01111000000000000000000000000000 27. 30 10000000000000000000000000000000 28. 1 01011000000000000000000000000000 29. 26 11000000000000000000000000000000 30. 3 00000000000000000000000000000000 31. 0</lang> Notice that the physical location of the pairs in storage can vary arbitrarily, and that (in this implementation) NIL is represented by zero. For an example showing how this list can be accessed, see Singly-Linked List (traversal)#SSEM.
Stata
There are several tasks in Rosetta Code all related to the linked-list structure. We will define here the required structure and all necessary functions, to make it easier to see how they are related to each over.
For instance, a stack and a queue are easily implemented with a linked-list:
- for a stack (LIFO), insert at head and pop at head,
- for a queue (FIFO), instert at tail and pop at head.
All the following is to be run in Mata.
Structures
Here we define two structures: one to hold a list item, another to hold the list pointers: we store both the head and the tail, in order to be able to insert an element at both ends. An empty list has both head and tail set to NULL.
<lang stata>struct item { transmorphic scalar value pointer(struct item scalar) scalar next }
struct list { pointer(struct item scalar) scalar head, tail }</lang>
Test if empty
<lang stata>real scalar list_empty(struct list scalar a) { return(a.head == NULL) }</lang>
Note that when a structure value is created, here for instance with a = list(), the elements are set to default values (zero real scalar, NULL pointer...). Hence, a newly created list is always empty.
Insertion
We can insert an element either before head or after tail. We can also insert after a given list item, but we must make sure the tail pointer of the list is updated if necessary.
<lang stata>void function list_insert(struct list scalar a, transmorphic scalar x) { struct item scalar i i.value = x if (a.head == NULL) { i.next = NULL a.head = a.tail = &i } else { i.next = a.head a.head = &i } }
void function list_insert_end(struct list scalar a, transmorphic scalar x) { struct item scalar i i.value = x i.next = NULL if (a.head==NULL) { a.head = a.tail = &i } else { (*a.tail).next = &i a.tail = &i } }
void function list_insert_after(struct list scalar a, pointer(struct item scalar) scalar p, transmorphic scalar x) {
struct item scalar i i.value = x i.next = (*p).next (*p).next = &i if (a.tail == p) { a.tail = &i } }</lang>
Traversal
Here are functions to compute the list length, and to print its elements. Here we assume list elements are either strings or real numbers, but one could write a more general function.
<lang stata>real scalar list_length(struct list scalar a) { real scalar n pointer(struct item scalar) scalar p
n = 0 for (p = a.head; p != NULL; p = (*p).next) { n++ } return(n) }
void list_show(struct list scalar a) { pointer(struct item scalar) scalar p
for (p = a.head; p != NULL; p = (*p).next) { if (eltype((*p).value) == "string") { printf("%s\n", (*p).value); } else { printf("%f\n", (*p).value); } } }</lang>
Return nth item
The function returns a pointer to the nth list item. If there are not enough elements, NULL is returned.
<lang stata>pointer(struct item scalar) scalar list_get(struct list scalar a, real scalar n) {
pointer(struct item scalar) scalar p real scalar i
p = a.head for (i = 1; p != NULL & i < n; i++) { p = (*p).next } return(p) }</lang>
Remove and return first element
The following function "pops" the first element of the list. If the list is empty, Mata will throw an error.
<lang stata>transmorphic scalar list_pop(struct list scalar a) { transmorphic scalar x if (a.head == NULL) { _error("empty list") } x = (*a.head).value if (a.head == a.tail) { a.head = a.tail = NULL } else { a.head = (*a.head).next } return(x) }</lang>
Remove and return nth element
<lang stata>transmorphic scalar list_remove(struct list scalar a, real scalar n) {
pointer(struct item scalar) scalar p, q real scalar i transmorphic scalar x
p = a.head if (n == 1) { if (p == NULL) { _error("empty list") } x = (*p).value if (p == a.tail) { a.head = a.tail = NULL } else { a.head = (*p).next } } else { for (i = 2; p != NULL & i < n; i++) { p = (*p).next } if (p == NULL) { _error("too few elements in list") } q = (*p).next if (q == NULL) { _error("too few elements in list") } x = (*q).value if (q == a.tail) { a.tail = p } (*p).next = (*q).next } return(x) }</lang>
Examples
Adding to the head:
<lang stata>a = list() list_insert(a, 10) list_insert(a, 20) list_insert(a, 30) list_length(a) list_show(a);</lang>
Output
30 20 10
Adding to the tail:
<lang stata>a = list() list_insert_end(a, 10) list_insert_end(a, 20) list_insert_end(a, 30) list_length(a) list_show(a);</lang>
Output
10 20 30
Adding after an element:
<lang stata>list_insert_after(a, list_get(a, 2), 40) list_show(a);</lang>
Output
10 20 40 30
Pop the first element:
<lang stata>list_pop(a)</lang>
Output
10
Linked-list task
<lang stata>a = list() list_insert_end(a, "A") list_insert_end(a, "B") list_insert_after(a, list_get(a, 1), "C") list_show(a)</lang>
Output
A C B
Stack behavior
<lang stata>a = list() for (i = 1; i <= 4; i++) { list_insert(a, i) } while (!list_empty(a)) { printf("%f\n", list_pop(a)) }</lang>
Output
4 3 2 1
Queue behavior
<lang stata>a = list() for (i = 1; i <= 4; i++) { list_insert_end(a, i) } while (!list_empty(a)) { printf("%f\n", list_pop(a)) }</lang>
Output
1 2 3 4
Swift
<lang swift>class Node<T>{
var data:T?=nil
var next:Node?=nil
init(input:T){
data=input
next=nil
}
} </lang>
Tcl
While it is highly unusual to implement linked lists in Tcl, since the language has a built-in list type (that internally uses arrays of references), it is possible to simulate it with objects.
or
<lang tcl>oo::class create List {
variable content next
constructor {value {list ""}} {
set content $value
set next $list
}
method value args {
set content {*}$args
}
method attach {list} {
set next $list
}
method detach {} {
set next ""
}
method next {} {
return $next
}
method print {} {
for {set n [self]} {$n ne ""} {set n [$n next]} {
lappend values [$n value]
}
return $values
}
}</lang>
X86 Assembly
This file will be included in the singly-linked list operation implementations <lang x86asm>
- x86_64 Linux NASM
- Linked_List_Definition.asm
%ifndef LinkedListDefinition %define LinkedListDefinition
struc link
value: resd 1 next: resq 1 linkSize:
endstruc
%endif </lang>
<lang asm>
struct link
.next: resd 1
.data: resd 1
endstruc
</lang>
Of course, ASM not natively having structures we can simply do..
<lang asm>
link resb 16
</lang>
Which would reserve 16 bytes(2 dwords). We could just simply think of it in the form of a structure.
<lang asm> link struct next dd ? data dd ? link ends </lang>
<lang asm>struc link next,data {
.next dd next .data dd data
}</lang>
XPL0
<lang XPL0>include c:\cxpl\codes; \intrinsic 'code' declarations def IntSize=4; \number of bytes in an integer def Size=10; \number of nodes in this linked list int Link, List, Node; [Link:= 0; \build linked list, starting at the end for Node:= 0 to Size-1 do
[List:= Reserve(IntSize*2); \get some memory to hold link and data
List(0):= Link;
List(1):= Node*Node; \insert example data
Link:= List; \Link now points to newly created node
];
Node:= List; \traverse the linked list repeat IntOut(0, Node(1)); CrLf(0); \display the example data
Node:= Node(0); \move to next node
until Node=0; \end of the list ]</lang>
zkl
Lists are a core element in zkl, both mutable and immutable. They are heterogeneous and can hold any object. They can be recursive. <lang zkl>List(1,"two",3.14); L(1,"two",3.14); ROList(fcn{"foobar"}); T('+);</lang>
- Programming Tasks
- Data Structures
- 360 Assembly
- AArch64 Assembly
- ACL2
- ActionScript
- Ada
- ALGOL 68
- ALGOL W
- ARM Assembly
- AutoHotkey
- AWK
- Axe
- BBC BASIC
- Bracmat
- C
- C++
- C sharp
- Clojure
- Common Lisp
- Clean
- D
- Delphi
- E
- Elena
- Erlang
- Factor
- Fantom
- Forth
- Fortran
- Go
- Groovy
- Haskell
- Icon
- Unicon
- J
- Java
- JavaScript
- Julia
- Kotlin
- Logo
- Mathematica
- Modula-2
- Modula-3
- Nanoquery
- Nim
- Objective-C
- OCaml
- Oforth
- OoRexx
- Pascal
- Perl
- Perl 6
- Phix
- PicoLisp
- PL/I
- Pop11
- PureBasic
- Python
- Racket
- REXX
- Ruby
- Rust
- Run BASIC
- Scala
- Scheme
- Sidef
- SSEM
- Stata
- Swift
- Tcl
- TclOO
- X86 Assembly
- XPL0
- Zkl
- GUISS/Omit