Singly-linked list/Element definition
From Rosetta Code
You are encouraged to solve this task according to the task description, using any language you may know.
Contents |
[edit] ActionScript
package
{
public class Node
{
public var data:Object = null;
public var link:Node = null;
public function Node(obj:Object)
{
data = obj;
}
}
}
[edit] Ada
type Link;
type Link_Access is access Link;
type Link is record
Next : Link_Access := null;
Data : Integer;
end record;
[edit] ALGOL 68
MODE DATA = STRUCT ( ... );
MODE LINK = STRUCT (
REF LINK next,
DATA value
);
[edit] AutoHotkey
element = 5 ; data
element_next = element2 ; link to next element
[edit] C
struct link {
struct link *next;
int data;
};
[edit] C++
The simplest C++ version looks basically like the C version:
struct link
{
link* next;
int data;
};
Initialization of links on the heap can be simplified by adding a constructor:
struct link
{
link* next;
int data;
link(int a_data, link* a_next = 0): next(a_next), data(a_data) {}
};
With this constructor, new nodes can be initialized directly at allocation; e.g. the following code creates a complete list with just one statement:
link* small_primes = new link(2, new link(3, new link(5, new link(7))));
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).
template<typename T> struct link
{
link* next;
T data;
link(T a_data, link* a_next = 0): next(a_next), data(a_data) {}
};
Note that the generic version works for any type, not only integral types.
[edit] C#
class Link
{
public int item;
public Link next;
}
[edit] Common Lisp
The built-in cons type is used to construct linked lists. Using another type would be unidiomatic and inefficient.
(cons 1 (cons 2 (cons 3 nil)) => (1 2 3)
[edit] Clean
import StdMaybe
:: Link t = { next :: Maybe (Link t), data :: t }
[edit] D
Generic template-based node element.
class Node(T) {
public:
T data;
Node next;
this(T d, Node n = null) { data=d; next=n; }
}
[edit] 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.
Type
pOneWayList = ^OneWayList;
OneWayList = record
pData : pointer ;
Next : pOneWayList ;
end;
[edit] 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
}
[edit] Factor
TUPLE: linked-list data next ;
: <linked-list> ( data -- linked-list )
linked-list new swap >>data ;
[edit] Forth
Idiomatically,
0 value numbers
: push ( n -- )
here swap numbers , , to numbers ;
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:
: 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 ;
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.
[edit] Fortran
In ISO Fortran 95 or later:
type node
real :: data
type( node ), pointer :: next => null()
end type node
!
!. . . .
!
type( node ) :: head
[edit] 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:
data List a = Nil | Cons a (List a)
A declaration like the one required in the task, with an integer as element type and a mutable link, would be
data IntList s = Nil | Cons Integer (STRef s (IntList s))
but that would be really awkward to use.
[edit] J
list=: 0 2$0
list
This creates and then displays an empty list, with zero elements. The first number in an item is (supposed to be) the index of the next element of the list (_ for the final element of the list). The second number in an item is the numeric value stored in that list item. The list is named and names are mutable in J which means links are mutable.
To create such a list with one element which contains number 42, we can do the following:
list=: ,: _ 42
list
_ 42
Now list contains one item, with index of the next item and value.
Note: this solution exploits the fact that, in this numeric case, data types for index and for node content are the same. If we need to store, for example, strings in the nodes, we should do something different, for example:
list=: 0 2$a: NB. creates list with 0 items
list
list=: ,: (<_) , <'some text' NB. creates list with 1 item
list
+-+---------+
|_|some text|
+-+---------+
[edit] Java
The simplest Java version looks basically like the C++ version:
class Link
{
Link next;
int data;
}
Initialization of links on the heap can be simplified by adding a constructor:
class Link
{
Link next;
int data;
Link(int a_data, Link a_next) { next = a_next; data = a_data; }
}
With this constructor, new nodes can be initialized directly at allocation; e.g. the following code creates a complete list with just one statement:
Link small_primes = new Link(2, new Link(3, new Link(5, new Link(7, null))));
Works with: Java version 1.5+ 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).
class Link<T>
{
Link<T> next;
T data;
Link(T a_data, Link<T> a_next) { next = a_next; data = a_data; }
}
[edit] 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]);
[edit] Logo
As with other list-based languages, simple lists are represented easily in 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"
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.
.setfirst list value
.setbf list remainder
[edit] Objective-C
This implements a class which has the primitive basic Objective-C class Object as parent.
#import <objc/Object.h>
@interface RCListElement : Object
{
RCListElement *next;
id datum;
}
+ (RCListElement *)new;
- (RCListElement *)next;
- (id)datum;
- (RCListElement *)setNext: (RCListElement *)nx;
- (void)setDatum: (id)d;
@end
@implementation RCListElement
+ (RCListElement *)new
{
RCListElement *m = [super new];
[m setNext: nil];
[m setDatum: nil];
return m;
}
- (RCListElement *)next
{
return next;
}
- (id)datum
{
return datum;
}
- (RCListElement *)setNext: (RCListElement *)nx
{
RCListElement *p;
p = next;
next = nx;
return p;
}
- (void)setDatum: (id)d
{
datum = d;
}
@end
[edit] 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:
type 'a list = Nil | Cons of 'a * 'a list
A declaration like the one required in the task, with an integer as element type and a mutable link, would be
type int_list = Nil | Cons of int * int_list ref
but that would be really awkward to use.
[edit] Pascal
type
PLink = ^TLink;
TLink = record
FNext: PLink;
FData: integer;
end;
[edit] 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.
my %node = (
data => 'say what',
next => \%foo_node,
);
$node{next} = \%bar_node; # mutable
[edit] 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'.
[edit] Pop11
List are built in into Pop11, so normally on would just use them:
;;; 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 =>
If however one wants to definite equivalent user-defined type, one can do this:
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 =>
[edit] PureBasic
Structure MyData
*next.MyData
Value.i
EndStructure
[edit] Python
The Node class implements also iteration for more Pythonic iteration over linked lists.
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
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.
[edit] 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])
[edit] 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:
(cons value next)
The value and next-link parts of the pair can be deconstructed using the car and cdr functions, respectively:
(car my-list) ; returns the first element of the list
(cdr my-list) ; returns the remainder of the list
Each of these parts are mutable and can be set using the set-car! and set-cdr! functions, respectively:
(set-car! my-list new-elem)
(set-cdr! my-list new-next)
[edit] 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.
Works with: Tcl version 8.6 or Library: TclOO
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
}
}
