Reverse a string
You are encouraged to solve this task according to the task description, using any language you may know.
Take a string and reverse it. For example, "asdf" becomes "fdsa".
For extra credit, preserve Unicode combining characters. For example, "as⃝df̅" becomes "f̅ds⃝a", not "̅fd⃝sa".
0815
This program reverses each line of its input. <lang 0815>}:r: Start reader loop.
!~>& Push a character to the "stack". <:a:=- Stop reading on newline.
^:r: @> Rotate the newline to the end and enqueue a sentinel 0. {~ Dequeue and rotate the first character into place. }:p:
${~ Print the current character until it's 0.
^:p:
- r: Read again.</lang>
- Output:
<lang bash>echo -e "foo\nbar" | 0815 rev.0 oof rab</lang>
8th
In 8th strings are UTF-8 and the language retains characters per-se: <lang forth> "abc" s:rev </lang>
- Output:
"cba"
ACL2
<lang Lisp>(reverse "hello")</lang>
ACL2 does not support unicode.
ActionScript
<lang ActionScript>function reverseString(string:String):String { var reversed:String = new String(); for(var i:int = string.length -1; i >= 0; i--) reversed += string.charAt(i); return reversed; }
function reverseStringCQAlternative(string:String):String { return string.split().reverse().join(); }</lang>
Ada
<lang ada>with Ada.Text_IO; use Ada.Text_IO;
procedure Reverse_String is
function Reverse_It (Item : String) return String is Result : String (Item'Range); begin for I in Item'range loop Result (Result'Last - I + Item'First) := Item (I); end loop; return Result; end Reverse_It;
begin
Put_Line (Reverse_It (Get_Line));
end Reverse_String;</lang>
Headline text
Agda
Using the Agda standard library, version 0.6. <lang agda2>module reverse_string where
open import Data.String open import Data.List
reverse_string : String → String reverse_string s = fromList (reverse (toList s))</lang>
Aime
<lang aime>text reverse(text s) {
data b; integer i;
i = length(s); while (i) { i -= 1; b_insert(b, -1, s[i]); }
return b_string(b);
}
integer main(void) {
o_text(reverse("Hello, World!")); o_byte('\n');
return 0;
}</lang>
ALGOL 68
<lang algol68>PROC reverse = (REF STRING s)VOID:
FOR i TO UPB s OVER 2 DO CHAR c = s[i]; s[i] := s[UPB s - i + 1]; s[UPB s - i + 1] := c OD;
main: (
STRING text := "Was it a cat I saw"; reverse(text); print((text, new line))
)</lang>
- Output:
was I tac a ti saW
APL
<lang apl> ⌽'asdf' fdsa</lang>
AppleScript
<lang AppleScript>reverseString("Hello World!")
on reverseString(str) reverse of characters of str as string end reverseString</lang>
Applesoft BASIC
<lang ApplesoftBasic>10 A$ = "THE FIVE BOXING WIZARDS JUMP QUICKLY" 20 GOSUB 100REVERSE 30 PRINT R$ 40 END
100 REMREVERSE A$ 110 R$ = "" 120 FOR I = 1 TO LEN(A$) 130 R$ = MID$(A$, I, 1) + R$ 140 NEXT I 150 RETURN</lang>
ATS
<lang ATS> // // How to compile: // patscc -DATS_MEMALLOC_LIBC -o string_reverse string_reverse.dats //
- include
"share/atspre_staload.hats"
fun string_reverse (
x: string
) : Strptr1 = let // val [n:int] x = g1ofg0(x) val y = string1_copy(x) val n = string1_length(x) val (pf, fpf | p) =
$UNSAFE.ptr_vtake{array(char,n)}(ptrcast(y))
val () = array_subreverse(!p, i2sz(0), n) prval () = fpf(pf) // in
$UNSAFE.castvwtp0{Strptr1}(y)
end (* end of [string_reverse] *)
(* ****** ****** *)
implement main0 () = let // val rev = string_reverse("asdf") val ((*void*)) = println! ("reverse(\"asdf\") = \"", rev, "\"") val ((*freed*)) = strptr_free (rev) // in
// nothing
end // end of [main0] </lang>
AutoHotkey
- "Normal" version:
<lang AutoHotkey>MsgBox % reverse("asdf")
reverse(string) {
Loop, Parse, string reversed := A_LoopField . reversed Return reversed
}</lang>
- A ''much'' slower version:
<lang AHK>Reverse(String){ ; credit to Rseding91
If (A_IsUnicode){ SLen := StrLen(String) * 2 VarSetCapacity(RString,SLen) Loop,Parse,String NumPut(Asc(A_LoopField),RString,SLen-(A_Index * 2),"UShort") } Else { SLen := StrLen(String) VarSetCapacity(RString,SLen) Loop,Parse,String NumPut(Asc(A_LoopField),RString,SLen-A_Index,"UChar") } VarSetCapacity(RString,-1) Return RString
}</lang>
AutoIt
<lang AutoIt>#AutoIt Version: 3.2.10.0 $mystring="asdf" $reverse_string = "" $string_length = StringLen($mystring)
For $i = 1 to $string_length
$last_n_chrs = StringRight($mystring, $i) $nth_chr = StringTrimRight($last_n_chrs, $i-1) $reverse_string= $reverse_string & $nth_chr
Next
MsgBox(0, "Reversed string is:", $reverse_string)</lang>
AWK
<lang awk>function reverse(s) {
p = "" for(i=length(s); i > 0; i--) { p = p substr(s, i, 1) } return p
}
BEGIN {
print reverse("edoCattesoR")
}</lang>
- Recursive
<lang awk>function reverse(s ,l) {
l = length(s) return l < 2 ? s:( substr(s,l,1) reverse(substr(s,1,l-1)) )
}
BEGIN {
print reverse("edoCattesoR")
}</lang>
- using split, then joining in front
<lang awk># Usage: awk -f reverse.awk -v s=Rosetta
function rev(s, i,a,r) {
split(s, a, "") for (i in a) r = a[i] r return r
} BEGIN {
if(!s) s = "Hello, world!" print s, "<-->", rev(s)
} </lang>
- Output:
Rosetta <--> attesoR
Babel
This example will handle UTF-8 encoded Unicode but doesn't handle combining characters. <lang babel>strrev: { str2ar ar2ls reverse ls2lf ar2str }</lang>
- str2ar - this operator converts a UTF-8 encoded string to an array of Unicode codepoints
- ar2ls - this operator converts the array to a linked-list
- reverse - this operator reverses a linked-list
- ls2lf - this operator undoes the effect of ar2ls
- ar2str - this operator undoes the effect of str2ar
BASIC
<lang qbasic>function reverse$(a$)
b$ = "" for i = 1 to len(a$) b$ = mid$(a$, i, 1) + b$ next i reverse$ = b$
end function</lang>
Batch File
<lang dos>@echo off setlocal enabledelayedexpansion call :reverse %1 res echo %res% goto :eof
- reverse
set str=%~1 set cnt=0
- loop
if "%str%" equ "" ( goto :eof ) set chr=!str:~0,1! set str=%str:~1% set %2=%chr%!%2! goto loop</lang>
BBC BASIC
<lang bbcbasic> PRINT FNreverse("The five boxing wizards jump quickly")
END DEF FNreverse(A$) LOCAL B$, C% FOR C% = LEN(A$) TO 1 STEP -1 B$ += MID$(A$,C%,1) NEXT = B$</lang>
Befunge
<lang befunge> ~>:#,_@ </lang>
Bracmat
<lang bracmat> ( reverse
= L x . :?L & @( !arg : ? ( %?x & utf$!x & !x !L:?L & ~` ) ? ) | str$!L )
& out$reverse$Ελληνικά</lang>
- Output:
άκινηλλΕ
Brainf***
<lang bf>[-]>,+[->,+]<[.<]</lang> The former wont stop taking input bytes unless a special compiler was made to stop at ENTER. The following checks for 10 ascii (line feed) and stops taking input at that point <lang bf>,----- ----- [+++++ +++++ > , ----- -----] If a newline is hit counter will be zero and input loop ends <[.<] run all chars backwards and print them
just because it looks good we print CRLF +++++ +++++ +++ . --- .</lang>
Brat
<lang brat>p "olleh".reverse #Prints "hello"</lang>
Burlesque
<lang burlesque> "Hello, world!"<- </lang>
C
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <locale.h>
- include <wchar.h>
const char *sa = "abcdef"; const char *su = "as⃝df̅"; /* Should be in your native locale encoding. Mine is UTF-8 */
int is_comb(wchar_t c) { if (c >= 0x300 && c <= 0x36f) return 1; if (c >= 0x1dc0 && c <= 0x1dff) return 1; if (c >= 0x20d0 && c <= 0x20ff) return 1; if (c >= 0xfe20 && c <= 0xfe2f) return 1; return 0; }
wchar_t* mb_to_wchar(const char *s) { wchar_t *u; size_t len = mbstowcs(0, s, 0) + 1; if (!len) return 0;
u = malloc(sizeof(wchar_t) * len); mbstowcs(u, s, len); return u; }
wchar_t* ws_reverse(const wchar_t* u) { size_t len, i, j; wchar_t *out; for (len = 0; u[len]; len++); out = malloc(sizeof(wchar_t) * (len + 1)); out[len] = 0; j = 0; while (len) { for (i = len - 1; i && is_comb(u[i]); i--); wcsncpy(out + j, u + i, len - i); j += len - i; len = i; } return out; }
char *mb_reverse(const char *in) { size_t len; char *out; wchar_t *u = mb_to_wchar(in); wchar_t *r = ws_reverse(u); len = wcstombs(0, r, 0) + 1; out = malloc(len); wcstombs(out, r, len); free(u); free(r); return out; }
int main(void) { setlocale(LC_CTYPE, "");
printf("%s => %s\n", sa, mb_reverse(sa)); printf("%s => %s\n", su, mb_reverse(su)); return 0; }</lang>
- Output:
abcdef => fedcba as⃝df̅ => f̅ds⃝a
<lang c>#include <glib.h> gchar *srev (const gchar *s) {
if (g_utf8_validate(s,-1,NULL)) { return g_utf8_strreverse (s,-1);
} } // main int main (void) {
const gchar *t="asdf"; const gchar *u="as⃝df̅"; printf ("%s\n",srev(t)); printf ("%s\n",srev(u)); return 0;
}</lang>
C++
<lang cpp>#include <iostream>
- include <string>
- include <algorithm>
int main() {
std::string s; std::getline(std::cin, s); std::reverse(s.begin(), s.end()); // modifies s std::cout << s << std::endl; return 0;
}</lang>
C#
C# does not have a built-in Reverse method for strings, which are immutable. One way to implement this is to convert the string to an array of characters, reverse that, and return a new string from the reversed array: <lang csharp>private static string ReverseString(string input) { char[] inputChars = input.ToCharArray(); Array.Reverse(inputChars); return new string(inputChars); }</lang> As of .Net 3.5 you can call LINQ's Reverse extension method on a string, since String implements the IEnumerable<char> interface. Because of this, the return type of Reverse is IEnumerable<char>. Fortunately, LINQ also provides the ToArray extension method, which can be used in conjunction with one of the constructors belonging to the String class which accepts an array of chars: <lang csharp>return new string(input.Reverse().ToArray());</lang>
Caché ObjectScript
USER>Write $Reverse("Hello, World") dlroW ,olleH
Clipper
Works with versions since 5, because LOCAL variables and the += operator was not implemented before. <lang Clipper>FUNCTION Reverse(sIn)
LOCAL sOut := "", i FOR i := Len(sIn) TO 1 STEP -1 sOut += Substr(sIn, i, 1) NEXT
RETURN sOut</lang>
Clojure
Basic reverse
For normal strings, the reverse function can be used to do the bulk of the work. However, it returns a character sequence, which has to be converted back to a string. <lang lisp>(defn str-reverse [s] (apply str (reverse s)))</lang>
Reverse words in a string
<lang lisp>(apply str (interpose " " (reverse (.split "the quick brown fox" " "))))</lang>
Supporting combining characters
Handling combining characters present a trickier task. We need to protect the relative ordering of the combining character and the character to its left. Thus, before reversing, the characters need to be grouped. <lang lisp>(defn combining? [c]
(let [type (Character/getType c)] ;; currently hardcoded to the types taken from the sample string (or (= type 6) (= type 7))))
(defn group
"Group normal characters with their combining characters" [chars] (cond (empty? chars) chars
(empty? (next chars)) (list chars) :else (let [dres (group (next chars))] (cond (combining? (second chars)) (cons (cons (first chars) (first dres)) (rest dres)) :else (cons (list (first chars)) dres)))))
(defn str-reverse
"Unicode-safe string reverse" [s] (apply str (apply concat (reverse (group s)))))</lang>
- Output:
user=> s "as⃝df̅" user=> (str-reverse s) "f̅ds⃝a"[ user=> (str-reverse (str-reverse s)) "as⃝df̅" user=>
COBOL
<lang cobol>FUNCTION REVERSE('QWERTY')</lang>
CoffeeScript
<lang javascript>"qwerty".split("").reverse().join ""</lang>
ColdFusion
You can reverse anything that can be written to the document in hashmarks (i.e. strings, numbers, now( ), etc.). <lang cfm><cfset myString = "asdf" /> <cfset myString = reverse( myString ) /></lang>
Common Lisp
<lang lisp>(reverse my-string)</lang>
Component Pascal
BlackBox Component Builder <lang oberon2> MODULE BbtReverseString; IMPORT StdLog;
PROCEDURE ReverseStr(str: ARRAY OF CHAR): POINTER TO ARRAY OF CHAR; VAR top,middle,i: INTEGER; c: CHAR; rStr: POINTER TO ARRAY OF CHAR; BEGIN NEW(rStr,LEN(str$) + 1); top := LEN(str$) - 1; middle := (top - 1) DIV 2; FOR i := 0 TO middle DO rStr[i] := str[top - i]; rStr[top - i] := str[i]; END; IF ODD(LEN(str$)) THEN rStr[middle + 1] := str[middle + 1] END; RETURN rStr; END ReverseStr;
PROCEDURE Do*;
VAR
x: CHAR;
BEGIN
StdLog.String("'asdf' reversed:> ");StdLog.String(ReverseStr("asdf"));StdLog.Ln
END Do;
END BbtReverseString.
</lang>
Execute: ^Q BbtReverseString.Do
- Output:
'asdf' reversed:> fdsa
D
<lang d>void main() { import std.range, std.conv;
string s1 = "hello"; // UTF-8 assert(s1.retro.text == "olleh");
wstring s2 = "hello"w; // UTF-16 assert(s2.retro.wtext == "olleh"w);
dstring s3 = "hello"d; // UTF-32 assert(s3.retro.dtext == "olleh"d);
// without using std.range: dstring s4 = "hello"d; assert(s4.dup.reverse == "olleh"d); // simple but inefficient (copies first, then reverses) }</lang>
Dart
Since Dart strings are sequences of UTF-16 code units, it would not be sufficient to simply reverse the characters in strings, as this would not work with UTF-16 surrogate pairs (pairs of UTF-16 code units that represent single characters outside the Unicode BMP). However, Dart provides a method to convert strings to sequences of unicode code points (called "runes" in Dart), and these sequences can easily be reversed and used to create new strings, so a string reversal function can be written with a single line of Dart code:
<lang dart>String reverse(String s) => new String.fromCharCodes(s.runes.toList().reversed);</lang>
A more complete example with unit tests would look like this:
<lang dart>import 'package:unittest/unittest.dart';
String reverse(String s) => new String.fromCharCodes(s.runes.toList().reversed);
main() {
group("Reverse a string -", () { test("Strings with ASCII characters are reversed correctly.", () { expect(reverse("hello, world"), equals("dlrow ,olleh")); }); test("Strings with non-ASCII BMP characters are reversed correctly.", () { expect(reverse("\u4F60\u4EEC\u597D"), equals("\u597D\u4EEC\u4F60")); }); test("Strings with non-BMP characters are reversed correctly.", () { expect(reverse("hello, \u{1F310}"), equals("\u{1F310} ,olleh")); }); });
}</lang>
Delphi
<lang Delphi>function ReverseString(const InString: string): string; var
i: integer;
begin
for i := Length(InString) downto 1 do Result := Result + InString[i];
end;</lang> You could also use this RTL function Introduced in Delphi 6: <lang Delphi>StrUtils.ReverseString</lang>
Déjà Vu
<lang dejavu>!print concat chars "Hello"</lang>
- Output:
olleH
DWScript
See Delphi.
E
<lang e>pragma.enable("accumulator") def reverse(string) {
return accum "" for i in (0..!(string.size())).descending() { _ + string[i] }
}</lang>
Emacs Lisp
<lang lisp>(concat (reverse (append "Hello World" nil)))</lang>
- Output:
"dlroW olleH"
Eiffel
<lang eiffel>class
APPLICATION
create
make
feature
make -- Demonstrate string reversal. do my_string := "Hello World!" my_string.mirror print (my_string) end my_string: STRING -- Used for reversal
end</lang>
- Output:
!dlroW olleH
EGL
<lang EGL>function reverse( str string ) returns( string ) result string; for ( i int from StrLib.characterLen( str ) to 1 decrement by 1 ) result ::= str[i:i]; end return( result ); end</lang>
Elixir
Elixir handles Unicode graphemes correctly by default. <lang elixir> IO.puts (String.reverse "asdf") IO.puts (String.reverse "as⃝df̅") </lang>
- Output:
fdsa f̅ds⃝a
Erlang
<lang erlang>1> lists:reverse("reverse!"). "!esrever"</lang> Erlang also supports binary strings, which uses its binary format. There is no standard function to reverse a binary sequence, but the following one does the job well enough. It works by changing the endianness (from little to big or the opposite) of the whole sequence, effectively reversing the string. <lang erlang>reverse(Bin) ->
Size = size(Bin)*8, <<T:Size/integer-little>> = Bin, <<T:Size/integer-big>>.</lang>
- Output:
1> test:reverse(<<"hello">>). <<"olleh">>
ERRE
<lang ERRE> PROGRAM REVERSE_STRING
PROCEDURE REVERSE(A$->R$)
LOCAL I% R$="" FOR I=1 TO LEN(A$) DO R$=MID$(A$,I,1)+R$ END FOR
END PROCEDURE
BEGIN
A$="THE FIVE BOXING WIZARDS JUMP QUICKLY" REVERSE(A$->R$) PRINT(R$)
END PROGRAM </lang>
Euler Math Toolbox
<lang Euler Math Toolbox> >function strrev (s) := chartostr(fliplr(strtochar(s))) >strrev("This is a test!")
!tset a si sihT
</lang>
Euphoria
<lang euphoria> include std/sequence.e printf(1, "%s\n", {reverse("abcdef") }) </lang>
Ezhil
<lang Ezhil>
- இந்த நிரல் தரப்படும் சரம் ஒன்றைத் தலைகீழாகத் திருப்பி அச்சிடும்
- உதாரணமாக "abc" என்ற சரம் தரப்பட்டால் அதனைத் திருப்பி "cba" என அச்சிடும்
- "எழில்" மொழியின்மூலம் இரண்டு வகைகளில் இதனைச் செய்யலாம். இரண்டு உதாரணங்களும் இங்கே தரப்பட்டுள்ளன
நிரல்பாகம் திருப்புக (சரம்1)
## முதல் வகை
சரம்2 = ""
@( சரம்1 இல் இ) ஒவ்வொன்றாக சரம்2 = இ + சரம்2 முடி
பின்கொடு சரம்2
முடி
நிரல்பாகம் மீண்டும்திருப்புக (சரம்1)
## இரண்டாம் வகை சரநீளம் = len(சரம்1) சரம்2 = ""
@(எண் = 0, எண் < சரநீளம், எண் = எண் + 1) ஆக
சரம்2 = எடு(சரம்1, எண்) + சரம்2
முடி
பின்கொடு சரம்2
முடி
அ = உள்ளீடு("ஓர் எழுத்துச் சரத்தைத் தாருங்கள் ")
பதிப்பி "நீங்கள் தந்த எழுத்துச் சரம்" அ
பதிப்பி "அதனை முதல் வகையில் திருப்பியுள்ளோம்: " திருப்புக(அ)
பதிப்பி "வேறொரு வகையில் திருப்பியுள்ளோம்: " மீண்டும்திருப்புக(அ)
</lang>
FBSL
A slow way <lang qbasic>Function StrRev1(ByVal $p1) dim $b = "" REPEAT len(p1) b = b & RIGHT(p1,1) p1 = LEFT(p1,LEN(p1)-1) END REPEAT return b End Function </lang>
A much faster (twice at least) way <lang qbasic>Function StrRev2(ByVal $p1) dim $b = "", %i for i = len(p1) DOWNTO 1 b = b & MID(p1,i,1) next return b End Function</lang>
An even faster way using PEEK, POKE, double-calls and quantity-in-hand <lang qbasic>Function StrRev3( $s ) FOR DIM x = 1 TO LEN(s) \ 2 PEEK(@s + LEN - x, $1) POKE(@s + LEN - x, s{x})(@s + x - 1, PEEK) NEXT RETURN s end function </lang>
An even faster way using the DynC (Dynamic C) mode <lang c>DynC StringRev($theString) As String
void rev(char *str) {
int len = strlen(str); char *HEAD = str; char *TAIL = str + len - 1; char temp; int i; for ( i = 0; i <= len / 2; i++, HEAD++, TAIL--) { temp = *HEAD; *HEAD = *TAIL; *TAIL = temp; }
} char *main(char* theString) { rev(theString); return theString; }
End DynC</lang>
Using DynASM, the Dynamic Assembler mode. <lang asm>DYNASM RevStr(BYVAL s AS STRING) AS STRING
// get length of string // divide by two // setup pointers to head and tail // iterate from 1 to (length \ 2) // swap head with tail // increment head pointer // decrement tail pointer
ENTER 0, 0 // = PUSH EBP: MOV EBP, ESP PUSH EBX // by Windows convention EBX, EDI, ESI must be saved before modification MOV EAX, s // get string pointer MOV ECX, EAX // duplicate it .WHILE BYTE PTR [ECX] <> 0
INC ECX // propagate to tail
.WEND MOV EDX, ECX // duplicate tail pointer DEC EDX // set it to last byte before trailing zero SUB ECX, EAX // get length in ECX in 1 CPU cycle SHR ECX, 1 // get length \ 2 in 1 CPU cycle; that's the beauty of power-of-two division
.WHILE ECX > 0 MOV BL, [EDX] // no need to XOR; just overwrite BL and BH contents MOV BH, [EAX] // DynAsm deduces data size from destination register sizes MOV [EDX], BH // ditto, source register sizes MOV [EAX], BL INC EAX // propagate pointers DEC EDX DEC ECX // decrement counter .WEND // point to start of string again MOV EAX, s // MOV = 1 CPU cycle, PUSH + POP = 2 CPU cycles POP EBX // by Windows convention ESI, EDI, EBX must be restored if modified LEAVE // = POP EBP RET
END DYNASM </lang>
F#
<lang fsharp>let ReverseString (s:string) = new string(Array.rev (s.ToCharArray()))</lang>
Factor
A string is a sequence and there is a default reverse implementation for those.
<lang factor>"hello" reverse</lang>
string-reverse
preserves graphemes:
<lang factor>"as⃝df̅" string-reverse "f̅ds⃝a" = .</lang>
FALSE
This solution does not take into account combination characters: <lang false>1_ [^$1_=~][]#% [$1_=~][,]#</lang> This solution does take into account combination characters (except for half-marks): <lang false>1_ [^$1_=~][
$$767>\879\>& 1ø$7615>\7620\>&| 1ø$8399>\8428\>&| [\]?
]#% [$1_=~][,]#</lang>
Fancy
<lang fancy>"hello world!" reverse</lang>
Forth
Method 1
<lang forth>: exchange ( a1 a2 -- )
2dup c@ swap c@ rot c! swap c! ;
- reverse ( c-addr u -- )
1- bounds begin 2dup > while 2dup exchange -1 /string repeat 2drop ;
s" testing" 2dup reverse type \ gnitset</lang>
Using the stack
<lang forth>\ reverse a counted string using the stack \ Method: Read the input string character by character onto the parameter stack \ Then write the character back into the same string from the stack
create mystring ," ABCDEFGHIJKLMNOPQRSTUVWXYZ987654321"
- pushstr ( str -- char[1].. char[n]) \ read the contents of STR onto the stack
count bounds do I c@ loop ;
- popstr ( char[1].. char[n] str -- ) \ read chars off stack into caddr
count bounds do I c! loop ;
- reverse ( str -- ) \ create the reverse function with the factored words
dup >r \ put a copy of the string addr on return stack pushstr \ push the characters onto the parameter stack r> popstr ; \ get back our copy of the string addr and pop the characters into it
\ test in the Forth console </lang>
output
mystring count type ABCDEFGHIJKLMNOPQRSTUVWXYZ987654321 ok mystring dup reverse count type 123456789ZYXWVUTSRQPONMLKJIHGFEDCBA ok
Fortran
<lang fortran>PROGRAM Example
CHARACTER(80) :: str = "This is a string" CHARACTER :: temp INTEGER :: i, length
WRITE (*,*) str length = LEN_TRIM(str) ! Ignores trailing blanks. Use LEN(str) to reverse those as well DO i = 1, length/2 temp = str(i:i) str(i:i) = str(length+1-i:length+1-i) str(length+1-i:length+1-i) = temp END DO WRITE(*,*) str
END PROGRAM Example</lang>
- Output:
This is a string gnirts a si sihT
Another implementation that uses a recursive not-in-place algorithm: <lang fortran>program reverse_string
implicit none character (*), parameter :: string = 'no devil lived on'
write (*, '(a)') string write (*, '(a)') reverse (string)
contains
recursive function reverse (string) result (res)
implicit none character (*), intent (in) :: string character (len (string)) :: res
if (len (string) == 0) then res = else res = string (len (string) :) // reverse (string (: len (string) - 1)) end if
end function reverse
end program reverse_string</lang>
- Output:
no devil lived on no devil lived on
Frink
The built-in reverse
function reverses a string or the elements of a list.
<lang frink>println[reverse["abcdef"]]</lang>
GAP
<lang gap>Reversed("abcdef");
- "fedcba"</lang>
Gema
Reverse each line in the input stream. Using built in function: <lang gema>\L=@reverse{$1}</lang> Not using built in function (recursively apply substring to same rule): <lang gema>\L<U1>=@{$2}$1</lang>
Go
Functions below assume UTF-8 encoding. (The task mentions Unicode but does not specify an encoding.) Strings in Go are not restricted to be UTF-8, but Go has good support for it and works with UTF-8 most natually. As shown below, certain string conversions work in UTF-8 and the range clause over a string works in UTF-8. Go also has a Unicode package in the standard library that makes easy work of recognizing combining characters for this task. <lang go>package main
import (
"fmt" "unicode" "unicode/utf8"
)
// no encoding func reverseBytes(s string) string {
r := make([]byte, len(s)) for i := 0; i < len(s); i++ { r[i] = s[len(s)-1-i] } return string(r)
}
// reverseCodePoints interprets its argument as UTF-8 and ignores bytes // that do not form valid UTF-8. return value is UTF-8. func reverseCodePoints(s string) string {
r := make([]rune, len(s)) start := len(s) for _, c := range s { // quietly skip invalid UTF-8 if c != utf8.RuneError { start-- r[start] = c } } return string(r[start:])
}
// reversePreservingCombiningCharacters interprets its argument as UTF-8 // and ignores bytes that do not form valid UTF-8. return value is UTF-8. func reversePreservingCombiningCharacters(s string) string {
if s == "" { return "" } p := []rune(s) r := make([]rune, len(p)) start := len(r) for i := 0; i < len(p); { // quietly skip invalid UTF-8 if p[i] == utf8.RuneError { i++ continue } j := i + 1 for j < len(p) && (unicode.Is(unicode.Mn, p[j]) || unicode.Is(unicode.Me, p[j]) || unicode.Is(unicode.Mc, p[j])) { j++ } for k := j - 1; k >= i; k-- { start-- r[start] = p[k] } i = j } return (string(r[start:]))
}
func main() {
test("asdf") test("as⃝df̅")
}
func test(s string) {
fmt.Println("\noriginal: ", []byte(s), s) r := reverseBytes(s) fmt.Println("reversed bytes:", []byte(r), r) fmt.Println("original code points:", []rune(s), s) r = reverseCodePoints(s) fmt.Println("reversed code points:", []rune(r), r) r = reversePreservingCombiningCharacters(s) fmt.Println("combining characters:", []rune(r), r)
}</lang>
- Output:
original: [97 115 100 102] asdf reversed bytes: [102 100 115 97] fdsa original code points: [97 115 100 102] asdf reversed code points: [102 100 115 97] fdsa combining characters: [102 100 115 97] fdsa original: [97 115 226 131 157 100 102 204 133] as⃝df̅ reversed bytes: [133 204 102 100 157 131 226 115 97] ��fd���sa original code points: [97 115 8413 100 102 773] as⃝df̅ reversed code points: [773 102 100 8413 115 97] ̅fd⃝sa combining characters: [102 773 100 115 8413 97] f̅ds⃝a
Groovy
Solution: <lang groovy>println "Able was I, 'ere I saw Elba.".reverse()</lang>
- Output:
.ablE was I ere' ,I saw elbA
Harbour
<lang visualfoxpro>FUNCTION Reverse( sIn )
LOCAL cOut := "", i
FOR i := Len( sIn ) TO 1 STEP -1 cOut += Substr( sIn, i, 1 ) NEXT
RETURN cOut</lang>
Haskell
<lang haskell>reverse = foldl (flip (:)) []</lang> This function as defined in the Haskell Prelude.
Supporting combining characters
<lang haskell>import Data.Char (isMark)
import Data.List (groupBy)
myReverse = concat . reverse . groupBy (const isMark)</lang>
groupBy (const isMark)
is an unusual way of splitting a string into its combined characters
HicEst
<lang hicest>CHARACTER string = "Hello World", tmp
L = LEN( string ) DO i = 1, L/2
tmp = string(i) string(i) = string(L-i+1) string(L-i+1) = tmp
ENDDO
WRITE(Messagebox, Name) string </lang>
Icon and Unicon
<lang Icon>procedure main(arglist) s := \arglist[1] | "asdf" write(s," <-> ", reverse(s)) # reverse is built-in end</lang>
Io
<lang io>"asdf" reverse</lang>
J
Reverse (|.) reverses a list of items (of any shape or type). <lang j> |.'asdf' fdsa</lang> Extra credit: First, a function to determine whether a Unicode character is a combining character: <lang j> ranges=.16b02ff 16b036f, 16b1dbf 16b1dff, 16b20cf 16b20ff, 16bfe1f 16bfe2f
iscombining=. 2 | ranges&I.</lang>
Then we need to box groups of letters and combining characters, reverse, and unbox. The boxing function can be carried out easily with dyad cut, which uses the indices of the ones on the right as the starting points for groups of characters. For clarity, its inverse will be defined as raze, which simply runs together the items inside boxes of its argument. <lang j> split=. (<;.1~ -.@iscombining) :. ;</lang>
After this, the solution is just to reverse under the split transformation. This also takes place under J code to convert from Unicode to integers. <lang j> |.&.split&.(3 u: 7&u:) 'as⃝df̅' f̅ds⃝a</lang>
Java
<lang java>public static String reverseString(String s) {
return new StringBuffer(s).reverse().toString();
}</lang>
<lang java5>public static String reverseString(String s) {
return new StringBuilder(s).reverse().toString();
}</lang>
JavaScript
<lang javascript>//using chained methods function reverseStr(s) {
return s.split().reverse().join();
}
//fast method using for loop function reverseStr(s) {
for (var i = s.length - 1, o = ; i >= 0; o += s[i--]) { } return o;
}
//fast method using while loop (faster with long strings in some browsers when compared with for loop) function reverseStr(s) {
var i = s.length, o = ; while (i--) o += s[i]; return o;
}</lang>
jq
jq's explode/implode filters are based on codepoints, and therefore "reverse_string" as defined here will reverse the sequence of codepoints. The topic of Unicode combining characters is a large one that is not touched on here. <lang jq>def reverse_string: explode | reverse | implode;</lang> Examples:
"nöel" | reverse_string # => "leön"
"as⃝df̅" | reverse_string # => "̅fd⃝sa"
Julia
<lang julia>julia> reverse("hey")
"yeh"</lang>
The reverse
function reverses codepoints (because this is the right behavior for the main application of string reversal: reversed string processing by external C libraries). However, starting in Julia 0.4, you can also reverse the graphemes if you want by:
<lang julia>julia> join(reverse(collect(graphemes("nöel"))))
"leön"</lang>
L++
<lang lisp>(include "string" "algorithm") (main
(decl std::string s) (std::getline std::cin s) (std::reverse (s.begin) (s.end)) (prn s))</lang>
LabVIEW
This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.
Lang5
<lang lang5>: flip "" split reverse "" join ; "qwer asdf" flip .</lang>
Lasso
<lang Lasso>local(input) = 'asdf'
- input->reverse</lang>
Using Query Expression & Array
More verbose than the string->reverse method, but this example illustrates different techniques to achieve the same result: using string->values to iterate over a string in order, inserting at position 1, and joining the resulting array as a string. <lang Lasso>local(input = 'asdf', output = array) with i in #input->values do #output->insertFirst(#i)
- output->join</lang>
LFE
Ordinary string: <lang lisp> > (lists:reverse "asdf") "fdsa" </lang>
Create a UTF-8 encoded string: <lang lisp> > (set encoded (binary ("åäö ð" utf8)))
- B(195 165 195 164 195 182 32 195 176)
</lang>
Display it, to be sure: <lang lisp> > (io:format "~tp~n" (list encoded)) <<"åäö ð"/utf8>> </lang>
Reverse it: <lang lisp> > (lists:reverse (unicode:characters_to_list encoded)) "ð öäå" </lang>
Liberty BASIC
<lang lb>input$ ="abcdefgABCDEFG012345" print input$ print ReversedStr$( input$)
end
function ReversedStr$(in$)
for i =len(in$) to 1 step -1 ReversedStr$ =ReversedStr$ +mid$( in$, i, 1) next i
end function</lang>
LiveCode
<lang livecode>function reverseString S
repeat with i = length(S) down to 1 put char i of S after R end repeat return R
end reverseString</lang>
Logo
REVERSE works on both words and lists. <lang logo>print reverse "cat ; tac</lang>
Lua
Built-in string.reverse(s) or s:reverse(). <lang lua>theString = theString:reverse()</lang>
M4
<lang m4>define(`invert',`ifelse(len(`$1'),0,,`invert(substr(`$1',1))'`'substr(`$1',0,1))')</lang>
Maple
<lang Maple>> StringTools:-Reverse( "foo" );
"oof"</lang>
Mathematica
<lang mathematica>StringReverse["asdf"]</lang>
MATLAB
A built-in function, "fliplr(string)" handles reversing a string of ASCII characters. Unicode is a whole other beast, if you need this functionality test to see if "fliplr()" properly handles the unicode characters you use. If it doesn't then you will need to code a function that is specific to your application.
Sample Usage: <lang MATLAB>>> fliplr(['She told me that she spoke English and I said great. '... 'Grabbed her hand out the club and I said lets skate.'])
ans =
.etaks s'tel dias I dna bulc eht tuo dnah reh debbarG .taerg dias I dna hsilgnE ekops ehs taht em dlot ehS</lang>
Maxima
<lang maxima>sreverse("abcdef"); /* "fedcba" */
sreverse("rats live on no evil star"); /* not a bug :o) */</lang>
MAXScript
<lang maxscript>fn reverseString s = (
local reversed = "" for i in s.count to 1 by -1 do reversed += s[i] reversed
)</lang>
Mirah
<lang mirah>def reverse(s:string)
StringBuilder.new(s).reverse
end
puts reverse('reversed')</lang>
Modula-3
<lang modula3>MODULE Reverse EXPORTS Main;
IMPORT IO, Text;
PROCEDURE String(item: TEXT): TEXT =
VAR result: TEXT := ""; BEGIN FOR i := Text.Length(item) - 1 TO 0 BY - 1 DO result := Text.Cat(result, Text.FromChar(Text.GetChar(item, i))); END; RETURN result; END String;
BEGIN
IO.Put(String("Foobarbaz") & "\n");
END Reverse.</lang>
- Output:
zabrabooF
MUMPS
<lang MUMPS>REVERSE
;Take in a string and reverse it using the built in function $REVERSE NEW S READ:30 "Enter a string: ",S WRITE !,$REVERSE(S) QUIT</lang>
- Output:
USER>D REVERSE^ROSETTA Enter a string: Hello, World! !dlroW ,olleH
Nemerle
Supporting Combining Characters
Compile with:
ncc -reference:System.Windows.Forms reverse.n
<lang Nemerle>using System; using System.Globalization; using System.Windows.Forms; using System.Console; using Nemerle.Utility.NString;
module StrReverse {
UReverse(text : string) : string { mutable output = []; def elements = StringInfo.GetTextElementEnumerator(text); while (elements.MoveNext()) output ::= elements.GetTextElement().ToString(); Concat("", output.Reverse()); } Main() : void { def test = "as⃝df̅"; MessageBox.Show($"$test --> $(UReverse(test))"); //for whatever reason my console didn't display Unicode properly, but a MessageBox worked }
}</lang>
Basic Reverse
Doesn't require the System.Globalization namespace, probably a little less overhead. <lang Nemerle>Reverse(text : string) : string {
mutable output = []; foreach (c in text.ToCharArray()) output ::= c.ToString(); Concat("", output)
}</lang>
NetRexx
<lang NetRexx>/* NetRexx */
options replace format comments java crossref savelog symbols nobinary
reverseThis = 'asdf' sihTesrever = reverseThis.reverse
say reverseThis say sihTesrever
return</lang>
- Output:
asdf fdsa
Nial
<lang nial>reverse 'asdf' =fdsa</lang>
Nim
<lang nim>import unicode
proc reverse(s: var string) =
for i in 0 .. s.high div 2: swap(s[i], s[s.high - i])
proc reversed(s: string): string =
result = newString(s.len) for i,c in s: result[s.high - i] = c
proc uniReversed(s: string): string =
result = newStringOfCap(s.len) var tmp: seq[Rune] = @[] for r in runes(s): tmp.add(r) for i in countdown(tmp.high, 0): result.add(toUtf8(tmp[i]))
proc isComb(r: Rune): bool =
(r >=% Rune(0x300) and r <=% Rune(0x36f)) or (r >=% Rune(0x1dc0) and r <=% Rune(0x1dff)) or (r >=% Rune(0x20d0) and r <=% Rune(0x20ff)) or (r >=% Rune(0xfe20) and r <=% Rune(0xfe2f))
proc uniReversedPreserving(s: string): string =
result = newStringOfCap(s.len) var tmp: seq[Rune] = @[] for r in runes(s): if isComb(r): tmp.insert(r, tmp.high) else: tmp.add(r) for i in countdown(tmp.high, 0): result.add(toUtf8(tmp[i]))
for str in ["Reverse This!", "as⃝df̅"]:
echo "Original string: ", str echo "Reversed: ", reversed(str) echo "UniReversed: ", uniReversed(str) echo "UniReversedPreserving: ", uniReversedPreserving(str)</lang>
- Output:
Original string: Reverse This! Reversed: !sihT esreveR UniReversed: !sihT esreveR UniReversedPreserving: !sihT esreveR Original string: as⃝df̅ Reversed: Ìfdâsa UniReversed: ‾fd⃝sa UniReversedPreserving: f̅ds⃝a
NewLISP
<lang NewLISP>(reverse "!dlroW olleH")</lang>
Objeck
<lang objeck> result := "asdf"->Reverse(); </lang>
Objective-C
This extends the NSString
object adding a reverseString
class method.
<lang objc>#import <Foundation/Foundation.h>
@interface NSString (Extended) -(NSString *)reverseString; @end
@implementation NSString (Extended) -(NSString *) reverseString {
NSUInteger len = [self length]; NSMutableString *rtr=[NSMutableString stringWithCapacity:len]; // unichar buf[1]; while (len > (NSUInteger)0) { unichar uch = [self characterAtIndex:--len]; [rtr appendString:[NSString stringWithCharacters:&uch length:1]]; } return rtr;
} @end</lang> Usage example: <lang objc>int main() {
@autoreleasepool { NSString *test = [@"!A string to be reverted!" reverseString]; NSLog(@"%@", test); } return 0;
}</lang>
Supporting combining characters
Extra credit <lang objc>#import <Foundation/Foundation.h>
@interface NSString (Extended) -(NSString *)reverseString; @end
@implementation NSString (Extended) -(NSString *)reverseString { NSInteger l = [self length] - 1; NSMutableString *ostr = [NSMutableString stringWithCapacity:[self length]]; while (l >= 0) { NSRange range = [self rangeOfComposedCharacterSequenceAtIndex:l]; [ostr appendString:[self substringWithRange:range]]; l -= range.length; } return ostr; } @end</lang> Usage example: <lang objc>int main() {
@autoreleasepool { NSString *test = [@"as⃝df̅" reverseString]; NSLog(@"%@", test); } return 0;
}</lang>
OCaml
Here a version that returns a new allocated string (preserving the original one): <lang ocaml>let rev_string str =
let len = String.length str in let res = String.create len in let last = len - 1 in for i = 0 to last do let j = last - i in res.[i] <- str.[j]; done; (res)</lang>
and here with in place modification: <lang ocaml>let rev_string str =
let last = String.length str - 1 in for i = 0 to last / 2 do let j = last - i in let c = str.[i] in str.[i] <- str.[j]; str.[j] <- c; done</lang>
here is a 100% functionnal string reversing function: <lang ocaml>let rec revs strin list index =
if List.length list = String.length strin then String.concat "" list else revs strin ((String.sub strin index 1)::list) (index+1)</lang>
revs "Hello World!" [] 0 will return "!dlroW olleH"
Octave
<lang octave>s = "a string"; rev = s(length(s):-1:1)</lang>
Oforth
<lang Oforth>reverse</lang>
OpenEdge/Progress
<lang Progress (OpenEdge ABL)>FUNCTION reverseString RETURNS CHARACTER (
INPUT i_c AS CHARACTER
):
DEFINE VARIABLE cresult AS CHARACTER NO-UNDO. DEFINE VARIABLE ii AS INTEGER NO-UNDO.
DO ii = LENGTH( i_c ) TO 1 BY -1: cresult = cresult + SUBSTRING( i_c, ii, 1 ). END. RETURN cresult.
END FUNCTION.
MESSAGE reverseString( "asdf" ) VIEW-AS ALERT-BOX.</lang>
OOC
<lang ooc> main: func {
"asdf" reverse() println() // prints "fdsa"
} </lang>
OxygenBasic
<lang oxygenbasic>
'8 BIT CHARACTERS
string s="qwertyuiop" sys a,b,i,j,le=len s ' for i=1 to le
j=le-i+1 if j<=i then exit for a=asc s,i b=asc s,j mid s,j,chr a mid s,i,chr b
next '
print s
'16 BIT CHARACTERS
wstring s="qwertyuiop" sys a,b,i,j,le=len s ' for i=1 to le
j=le-i+1 if j<=i then exit for a=unic s,i b=unic s,j mid s,j,wchr a mid s,i,wchr b
next ' print s </lang>
OxygenBasic x86 Assembler
32 bit code, 8-bit characters: <lang oxygenbasic>
string s="qwertyuiop" sys p=strptr s, le=len s mov esi,p mov edi,esi add edi,le dec edi (
cmp esi,edi jge exit mov al,[esi] mov ah,[edi] mov [esi],ah mov [edi],al inc esi dec edi repeat
)
print s </lang>
Oz
Strings are lists. A function "Reverse" defined on lists is part of the implementation. <lang oz>{System.showInfo {Reverse "!dlroW olleH"}}</lang> An efficient (tail-recursive) implementation could look like this: <lang oz>local
fun {DoReverse Xs Ys} case Xs of nil then Ys [] X|Xr then {DoReverse Xr X|Ys} end end
in
fun {Reverse Xs} {DoReverse Xs nil} end
end</lang> Oz uses a single-byte encoding by default. If you decide to use a multi-byte encoding, Reverse will not work correctly.
PARI/GP
<lang parigp>reverse(s)=concat(Vecrev(s))</lang>
Pascal
The following examples handle correctly only single-byte encodings.
Standard Pascal
The following only works on implementations which implement Level 1 of standard Pascal (many popular compilers don't).
Standard Pascal doesn't have a separate string type, but uses arrays of char for strings. Note that Standard Pascal doesn't allow a return type of char array, therefore the destination array is passed through a var parameter (which is more efficient anyway). <lang pascal>{ the result array must be at least as large as the original array } procedure reverse(s: array[min .. max: integer] of char, var result: array[min1 .. max1: integer] of char);
var i, len: integer; begin len := max-min+1; for i := 0 to len-1 do result[min1 + len-1 - i] := s[min + i] end;</lang>
<lang pascal>{Copy and paste it in your program} function revstr(my_s:string):string;
var out_s:string; ls,i:integer; begin ls:=length(my_s); for i:=1 to ls do out_s:=out_s+my_s[ls-i+1]; revstr:=out_s; end;</lang>
Extended Pascal, Turbo Pascal, Delphi and compatible compilers
<lang pascal>function reverse(s:string):string; var i:integer; var tmp:char; begin
for i:=1 to length(s) div 2 do begin tmp:=s[i]; s[i]:=s[length(s)+1-i]; s[length(s)+1-i]:=tmp; reverse:=s; end;
end;</lang> alternative as procedure which changes the original <lang pascal>procedure revString(var s:string); var
i,j:integer; tmp:char;
begin
i := 1; j := length(s); while i<j do begin tmp:=s[i]; s[i]:=s[j]; s[j]:=tmp; inc(i); dec(j) end;
end;</lang>
Perl
This reverses characters (code points): <lang perl>$string = "visor"; $flip = reverse $string; # becomes "rosiv"</lang>
This reverses graphemes: <lang perl>$string = "Jose\x{301}"; # "José" in NFD $flip = join("", reverse $string =~ /\X/g); # becomes "ésoJ"</lang>
Perl 6
<lang perl6># Not transformative. my $reverse = flip $string;
- or
say "hello world".flip;</lang> Perl 6 is specced to work on graphemes by default, but current implementations are limited to processing codepoints.
PHP
<lang php>strrev($string);</lang>
If you want Unicode support, you have to use some multibyte function. Sadly, PHP doesn't contain mb_strrev()
. One of functions which support Unicode and is useful in this case is preg_split()
.
<lang php>// Will split every Unicode character to array, reverse array and will convert it to string.
join(, array_reverse(preg_split('""u', $string, -1, PREG_SPLIT_NO_EMPTY)));</lang>
PicoLisp
<lang PicoLisp>(pack (flip (chop "äöüÄÖÜß")))</lang>
- Output:
-> "ßÜÖÄüöä"
PL/I
<lang PL/I>s = reverse(s);</lang>
Pop11
<lang pop11>define reverse_string(s);
lvars i, l = length(s); for i from l by -1 to 1 do s(i); endfor; consstring(l);
enddefine;</lang>
PostScript
The following implementation works on arrays of numerics as well as characters ( string ). <lang PostScript>/reverse{ /str exch def /temp str 0 get def /i 0 def str length 2 idiv{ /temp str i get def str i str str length i sub 1 sub get put str str length i sub 1 sub temp put /i i 1 add def }repeat str pstack }def</lang>
- Output:
<lang PostScript>[1 2 3] reverse % input [3 2 1]
(Hello World) reverse % input (dlroW olleH)</lang>
PowerShell
Test string <lang powershell>$s = "asdf"</lang>
Array indexing
Creating a character array from the end to the string's start and join it together into a string again.
<lang powershell>[string]::Join(, $s[$s.Length..0])</lang>
<lang powershell>-join ($s[$s.Length..0])</lang>
<lang powershell>[array]::Reverse($s)</lang>
Regular expressions
Creating a regular expression substitution which captures every character of the string in a capture group and uses a reverse-ordered string of references to those to construct the reversed string.
<lang powershell>$s -replace
('(.)' * $s.Length), [string]::Join(, ($s.Length..1 | ForEach-Object { "`$$_" }))</lang>
<lang powershell>$s -replace
('(.)' * $s.Length), -join ($s.Length..1 | ForEach-Object { "`$$_" } )</lang>
Prolog
<lang prolog>reverse("abcd", L), string_to_list(S,L).</lang>
- Output:
L = [100,99,98,97], S = "dcba".
The main workings are hidden inside the reverse/2 predicate, so lets write one to see how it works: <lang prolog>accRev([H|T], A, R) :- accRev(T, [H|A], R). accRev([], A, A).
rev(L,R) :- accRev(L,[],R).</lang>
Protium
Padded out, variable length Chinese dialect <lang html><# 显示 指定 变量 反转顺序 字串>集装箱|猫坐在垫子</#></lang>
This assigns the reverse of 'the cat sat on the mat' to the variable 'container' and displays the result which is
子垫在坐猫
which Google Translate renders as
Sub-pad sitting cat
.
The same again but with everything in Korean. <lang html><# 보이십 할당하 변물건 열거꾸 문자그>컨테이너|고양이가 매트 위에 앉아</#></lang>
Reversing the Korean makes an untranslatable-by-Google mess of the sentence, viz
아앉 에위 트매 가이양고
.
The short-opcode version in English dialect is <lang html><@ SAYLETVARREVLIT>集装箱|猫坐在垫子</@></lang> Protium works in Unicode.
PureBasic
<lang PureBasic>Debug ReverseString("!dekrow tI")</lang>
Python
Optimized for user input
<lang python>raw_input()[::-1]</lang>
Already known string
<lang python>string[::-1]</lang>
Unicode reversal
(See this article for more information) <lang python>
Reverse a Unicode string with proper handling of combining characters
import unicodedata
def ureverse(ustring):
Reverse a string including unicode combining characters
Example: >>> ucode = .join( chr(int(n, 16)) for n in ['61', '73', '20dd', '64', '66', '305'] ) >>> ucoderev = ureverse(ucode) >>> ['%x' % ord(char) for char in ucoderev] ['66', '305', '64', '73', '20dd', '61'] >>> groupedchars = [] uchar = list(ustring) while uchar: if 'COMBINING' in unicodedata.name(uchar[0], ): groupedchars[-1] += uchar.pop(0) else: groupedchars.append(uchar.pop(0)) # Grouped reversal groupedchars = groupedchars[::-1]
return .join(groupedchars)
if __name__ == '__main__':
ucode = .join( chr(int(n, 16)) for n in ['61', '73', '20dd', '64', '66', '305'] ) ucoderev = ureverse(ucode) print (ucode) print (ucoderev)</lang>
Qi
It's simplest just to use the common lisp REVERSE function. <lang Qi>(REVERSE "ABCD")</lang>
R
The following code works with UTF-8 encoded strings too. <lang R>revstring <- function(stringtorev) {
return( paste( strsplit(stringtorev,"")1[nchar(stringtorev):1] ,collapse="") )
}</lang>
Alternatively (using rev() function):
<lang R> revstring <- function(s) paste(rev(strsplit(s,"")1),collapse="")</lang>
<lang R>revstring("asdf") revstring("m\u00f8\u00f8se") Encoding("m\u00f8\u00f8se") # just to check if on your system it's something
# different!</lang>
- Output:
[1] "fdsa" [1] "esøøm" [1] "UTF-8"
R can encode strings in Latin1 and UTF-8 (the default may depend on the locale); the Encoding(string) can be used to know if the string is encoded in Latin1 or UTF-8; the encoding can be forced (Encoding(x) <- "latin1"), or we can use iconv to properly translate between encodings whenever possible.
Rascal
<lang rascal>import String; reverse("string")</lang>
Racket
As in Scheme:
<lang Racket>#lang racket
(define (string-reverse s)
(list->string (reverse (string->list s))))
(string-reverse "aoeu")</lang>
- Output:
Welcome to DrRacket, version 5.3.3.5--2013-02-20(5eddac74/d) [3m]. Language: racket; memory limit: 512 MB. "ueoa" >
RapidQ
<lang vb> print reverse$("This is a test") </lang>
Raven
<lang Raven>"asdf" reverse</lang>
- Output:
fdsa
REBOL
<lang REBOL>print reverse "asdf"</lang> Note the string is reversed in place. If you were using it anywhere else, you would find it reversed: <lang REBOL>x: "asdf" print reverse x print x ; Now reversed.</lang> REBOL/View 2.7.6.3.1 14-Mar-2008 does not handle Unicode strings. This is planned for REBOL 3.
Retro
<lang Retro>with strings' "asdf" reverse puts</lang>
REXX
All methods shown below also work with NULL values.
using REVERSE bif
<lang rexx>/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!' string2 = reverse(string1)
say ' original string: ' string1 say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</lang>
output
original string: A man, a plan, a canal, Panama! reversed string: !amanaP ,lanac a ,nalp a ,nam A
using SUBSTR bif, left to right
<lang rexx>/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!' string2 =
do j=1 for length(string1) string2 = substr(string1,j,1)string2 end /*j*/
say ' original string: ' string1 say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</lang>
output is identical to the 1st version.
(Regarding the previous example) Another method of coding an abutment (an implied concatenation) is:
<lang rexx> string2 = substr(string1,j,1) || string2
/*───── or ─────*/ string2=substr(string1,j,1)||string2</lang>
using SUBSTR bif, right to left
<lang rexx>/*REXX program to reverse a string (and show before and after strings).*/
string1 = 'A man, a plan, a canal, Panama!' string2 =
do j=length(string1) to 1 by -1 string2 = string2 || substr(string1,j,1) end /*j*/
say ' original string: ' string1 say ' reversed string: ' string2
/*stick a fork in it, we're done.*/</lang>
output is identical to the 1st version.
RLaB
<lang RLaB>>> x = "rosettacode" rosettacode
// script rx = ""; for (i in strlen(x):1:-1) {
rx = rx + substr(x, i);
}
>> rx edocattesor</lang>
Ruby
<lang ruby>str = "asdf" reversed = str.reverse</lang> or <lang ruby>#encoding: utf-8 "résumé niño".reverse #=> "oñin émusér"</lang>
Run BASIC
<lang runbasic>string$ = "123456789abcdefghijk" for i = len(string$) to 1 step -1
print mid$(string$,i,1);
next i</lang>
Rust
<lang rust> extern crate unicode_segmentation; use unicode_segmentation::UnicodeSegmentation;
fn main() {
let s = "一二三四五六七八九十"; let s2 = "as⃝df̅"; let reversed: String = s.chars().rev().collect(); let reversed2: String = UnicodeSegmentation::graphemes(s2, true) .rev().collect(); println!("{}", reversed); println!("{}", reversed2);
}</lang>
- Output:
十九八七六五四三二一
f̅ds⃝a
SAS
<lang sas>data _null_; length a b $11; a="I am Legend"; b=reverse(a); put a; put b; run;</lang>
Sather
<lang sather>class MAIN is
main is s ::= "asdf"; reversed ::= s.reverse; -- current implementation does not handle multibyte encodings correctly end;
end;</lang>
Scala
Easy way: <lang scala>"asdf".reverse</lang>
Slightly less easy way: <lang scala>"asdf".foldRight("")((a,b) => b+a)</lang>
Unicode-aware, method 1:
<lang scala>def reverse(s: String) = {
import java.text.{Normalizer,BreakIterator} val norm = Normalizer.normalize(s, Normalizer.Form.NFKC) // waffle -> waffle (optional) val it = BreakIterator.getCharacterInstance it setText norm def break(it: BreakIterator, prev: Int, result: List[String] = Nil): List[String] = it.next match { case BreakIterator.DONE => result case cur => break(it, cur, norm.substring(prev, cur) :: result) } break(it, it.first).mkString
}</lang>
- Output:
scala> reverse("as⃝df̅") res0: String = f̅ds⃝a
Unicode-aware, method 2: I can't guarantee it get all the cases, but it does work with combining characters as well as supplementary characters. I did not bother to preserve the order of newline characters, and I didn't even consider directionality beyond just ruling it out. <lang scala>def reverseString(s: String) = {
import java.lang.Character._ val combiningTypes = List(NON_SPACING_MARK, ENCLOSING_MARK, COMBINING_SPACING_MARK) def isCombiningCharacter(c: Char) = combiningTypes contains c.getType def isCombiningSurrogate(high: Char, low: Char) = combiningTypes contains getType(toCodePoint(high, low)) def isCombining(l: List[Char]) = l match { case List(a, b) => isCombiningSurrogate(a, b) case List(a) => isCombiningCharacter(a) case Nil => true case _ => throw new IllegalArgumentException("isCombining expects a list of up to two characters") } def cleanSurrogate(l: List[Char]) = l match { case List(a, b) if a.isHighSurrogate && b.isLowSurrogate => l case List(a, b) if a.isLowSurrogate => Nil case List(a, b) => List(a) case _ => throw new IllegalArgumentException("cleanSurrogate expects lists of two characters, exactly") } def splitString(string: String) = (string+" ").iterator sliding 2 map (_.toList) map cleanSurrogate toList
def recurse(fwd: List[List[Char]], rev: List[Char]): String = fwd match { case Nil => rev.mkString case c :: rest => val (combining, remaining) = rest span isCombining recurse(remaining, c ::: combining.foldLeft(List[Char]())(_ ::: _) ::: rev) } recurse(splitString(s), Nil)
}</lang> REPL on Windows doesn't handle Unicode, so I'll show the bytes instead:
scala> res71 map ("\\u%04x" format _.toInt) res80: scala.collection.immutable.IndexedSeq[String] = IndexedSeq(\u0061, \u0073, \u20dd, \u0064, \u0066, \u0305) scala> reverseString(res71) map ("\\u%04x" format _.toInt) res81: scala.collection.immutable.IndexedSeq[String] = IndexedSeq(\u0066, \u0305, \u0064, \u0073, \u20dd, \u0061)
Scheme
<lang scheme>(define (string-reverse s)
(list->string (reverse (string->list s))))</lang>
> (string-reverse "asdf") "fdsa"
Scratch
Sed
<lang sed>#!/bin/sed -f
/../! b
- Reverse a line. Begin embedding the line between two newlines
s/^.*$/\ &\ /
- Move first character at the end. The regexp matches until
- there are zero or one characters between the markers
tx
- x
s/\(\n.\)\(.*\)\(.\n\)/\3\2\1/ tx
- Remove the newline markers
s/\n//g</lang>
Seed7
Seed7 strings are encoded with UTF-32 therefore no special Unicode solution is necessary <lang seed7>$ include "seed7_05.s7i";
const func string: reverse (in string: stri) is func
result var string: result is ""; local var integer: index is 0; begin for index range length(stri) downto 1 do result &:= stri[index]; end for; end func;
const proc: main is func
begin writeln(reverse("Was it a cat I saw")); end func;</lang>
- Output:
was I tac a ti saW
Sidef
<lang ruby>"asdf".reverse; # fdsa "résumé niño".reverse; # oñin émusér</lang>
Self
In-place reversal: <lang self>'asdf' copyMutable reverse</lang>
Slate
In-place reversal: <lang slate>'asdf' reverse</lang> Non-destructive reversal: <lang slate>'asdf' reversed</lang>
Smalltalk
<lang smalltalk>'asdf' reverse</lang>
the above does inplace, destructive reverse. It is usually better to use <lang smalltalk>'asdf' reversed</lang> which returns a new string.
SNOBOL4
ASCII-only <lang snobol> output = reverse(reverse("reverse")) end</lang>
- Output:
reverse
Standard ML
<lang sml>val str_reverse = implode o rev o explode; val string = "asdf"; val reversed = str_reverse string;</lang>
Swift
Swift's strings are iterated by Character
s, which represent "Unicode grapheme clusters", so reversing it reverses it with combining characters too:
<lang swift>func reverseString(s: String) -> String {
return String(s.characters.reverse())
} print(reverseString("asdf")) print(reverseString("as⃝df̅"))</lang>
<lang swift>func reverseString(s: String) -> String {
return String(reverse(s))
} println(reverseString("asdf")) println(reverseString("as⃝df̅"))</lang>
- Output:
fdsa f̅ds⃝a
Tcl
<lang tcl>package require Tcl 8.5 string reverse asdf</lang>
TI-83 BASIC
Note: length( and sub( can be found in the catalog. <lang ti83b>:Str1
- For(I,1,length(Ans)-1
- sub(Ans,2I,1)+Ans
- End
- sub(Ans,1,I→Str1</lang>
Turing
<lang Turing> % Reverse a string
var input : string (100)
put "Enter a string to reverse: " .. get input
var count : int := length(input) loop
if count >= 1 then put input(count) .. else exit end if count := count - 1
end loop </lang>
TUSCRIPT
<lang tuscript>$$ MODE TUSCRIPT SET input="was it really a big fat cat i saw" SET reversetext=TURN (input) PRINT "before: ",input PRINT "after: ",reversetext</lang>
- Output:
before: was it really a big fat cat i saw after: was i tac taf gib a yllaer ti saw
UNIX Shell
<lang bash>
- !/bin/bash
str=abcde
for((i=${#str}-1;i>=0;i--)); do rev="$rev${str:$i:1}"; done
echo $rev </lang>
or
<lang bash> str='i43go1342iu 23iu4o 23iu14i324y 2i13' rev <<< "$str"
- rev is not built-in function, though is in /usr/bin/rev
</lang>
Unlambda
Reverse the whole input: <lang Unlambda>``@c`d``s`|k`@c</lang>
Ursala
<lang Ursala>#import std
- cast %s
example = ~&x 'asdf'
verbose_example = reverse 'asdf'</lang>
- Output:
'fdsa'
VBA
Non-recursive version
<lang VBA>Public Function Reverse(aString as String) as String ' returns the reversed string dim L as integer 'length of string dim newString as string
newString = "" L = len(aString) for i = L to 1 step -1
newString = newString & mid$(aString, i, 1)
next Reverse = newString End Function</lang>
Recursive version
<lang VBA>Public Function RReverse(aString As String) As String 'returns the reversed string 'do it recursively: cut the string in two, reverse these fragments and put them back together in reverse order Dim L As Integer 'length of string Dim M As Integer 'cut point
L = Len(aString) If L <= 1 Then 'no need to reverse
RReverse = aString
Else
M = Int(L / 2) RReverse = RReverse(Right$(aString, L - M)) & RReverse(Left$(aString, M))
End If End Function</lang>
Example dialogue
print Reverse("Public Function Reverse(aString As String) As String") gnirtS sA )gnirtS sA gnirtSa(esreveR noitcnuF cilbuP print RReverse("Sunday Monday Tuesday Wednesday Thursday Friday Saturday Love") evoL yadrutaS yadirF yadsruhT yadsendeW yadseuT yadnoM yadnuS print RReverse(Reverse("I know what you did last summer")) I know what you did last summer
VBScript
<lang VBScript> WScript.Echo StrReverse("asdf") </lang>
Vedit macro language
This routine reads the text from current line, reverses it and stores the reversed string in text register 10: <lang vedit>Reg_Empty(10) for (BOL; !At_EOL; Char) {
Reg_Copy_Block(10, CP, CP+1, INSERT)
}</lang> This routine reverses the current line in-place: <lang vedit>BOL while (!At_EOL) {
Block_Copy(EOL_pos-1, EOL_pos, DELETE)
}</lang>
Visual Basic .NET
<lang vbnet> Function Reverse(ByVal s As String) As String
Dim t() as Char = s.toCharArray Array.reverse(t) Return new String(t) End Function</lang>
Wart
<lang wart>(rev "asdf")</lang>
Wart doesn't support unicode yet.
Wortel
<lang wortel>; the @rev operator reverses strings and arrays @rev "abc" ; returns "cba"
- or the same thing using a pointer expression
!~r "abc"</lang>
XPL0
<lang XPL0>include c:\cxpl\codes; \intrinsic 'code' declarations string 0; \use zero-terminated strings, instead of MSb terminated
func StrLen(Str); \Return the number of characters in an ASCIIZ string char Str; int I; for I:= 0 to -1>>1-1 do
if Str(I) = 0 then return I;
func RevStr(S); \Reverse the order of the bytes in a string char S; int L, I, T; [L:= StrLen(S); for I:= 0 to L/2-1 do
[T:= S(I); S(I):= S(L-I-1); S(L-I-1):= T];
return S; ];
[Text(0, RevStr("a")); CrLf(0);
Text(0, RevStr("ab")); CrLf(0); Text(0, RevStr("abc")); CrLf(0); Text(0, RevStr("Able was I ere I saw Elba.")); CrLf(0);
]</lang>
Output:
a ba cba .ablE was I ere I saw elbA
Yorick
This only handles ASCII characters. It works by converting a string to an array of char; dropping the last character (which is the null byte); reversing the order of the characters; then converting back to a string. <lang yorick>strchar(strchar("asdf")(:-1)(::-1))</lang>
zkl
These only handle ASCII characters, no extra credit.
"this is a test".reverse()
Old school ways to do it:
Build by prepending characters, creates n strings:
"this is a test".reduce(fcn(p,c){c+p})
Convert to list, reverse, convert back to string:
"this is a test".split("").reverse().concat()
Write to a byte buffer and convert to string:
"this is a test".pump(Void,Data().insert.fp(0)).text
The ".fp(0)" creates a closure so each character is fed to data.insert(0,c). pump is a method that sends each character to a function to a sink (in this case /dev/null). The output is the result of the last call, which is data.insert which is self/data.
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