Run-length encoding
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You are encouraged to solve this task according to the task description, using any language you may know.
- Task
Given a string containing uppercase characters (A-Z), compress repeated 'runs' of the same character by storing the length of that run, and provide a function to reverse the compression.
The output can be anything, as long as you can recreate the input with it.
- Example
- Input:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW - Output:
12W1B12W3B24W1B14W
Note: the encoding step in the above example is the same as a step of the Look-and-say sequence.
11l
F encode(input_string)
V count = 1
V prev = Char("\0")
[(Char, Int)] lst
L(character) input_string
I character != prev
I prev != Char("\0")
lst.append((prev, count))
count = 1
prev = character
E
count++
lst.append((input_string.last, count))
R lst
F decode(lst)
V q = ‘’
L(character, count) lst
q ‘’= character * count
R q
V value = encode(‘aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa’)
print(‘Encoded value is ’value.map(v -> String(v[1])‘’v[0]))
print(‘Decoded value is ’decode(value))- Output:
Encoded value is [5a, 6h, 7m, 1u, 7i, 6a] Decoded value is aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa
8086 Assembly
Output is in hexadecimal but is otherwise correct.
.model small ; 128k .exe file
.stack 1024 ; load SP with 0400h
.data ; no data segment needed
.code
start:
mov ax,@code
mov ds,ax
mov es,ax
mov si,offset TestString
mov di,offset OutputRam
cld
compressRLE:
lodsb
cmp al,0 ;null terminator?
jz finished_Compressing ;if so, exit
push di
push si
mov cx,0FFFFh ;exit after 65536 reps or the run length ends.
xchg di,si ;scasb only works with es:di so we need to exchange
repz scasb ;repeat until [es:di] != AL
xchg di,si ;exchange back
pop dx ;pop the old SI into DX instead!
pop di
push si
sub si,dx
mov dx,si
pop si
;now the run length is in dx, store it into output ram.
push ax
mov al,dl
stosb
pop ax
stosb ;store the letter that corresponds to the run
dec si ;we're off by one, so we need to correct for that.
jmp compressRLE ;back to start
finished_Compressing:
mov bp, offset OutputRam
mov bx, 32
call doMemDump ;displays a hexdump of the contents of OutputRam
mov ax,4C00h
int 21h ;exit DOS
TestString byte "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",0
OutputRam byte 256 dup (0)
end start
- Output:
0C 57 01 42 0C 57 03 42 .W.B.W.B 18 57 01 42 0E 57 00 00 .W.B.W.. 00 00 00 00 00 00 00 00 ........ 00 00 00 00 00 00 00 00 ........
The hexdump above converts to: 12W 1B 12W 3B 24W 1B 14W
Action!
BYTE FUNC GetLength(CHAR ARRAY s BYTE pos)
CHAR c
BYTE len
c=s(pos)
len=1
DO
pos==+1
IF pos<=s(0) AND s(pos)=c THEN
len==+1
ELSE
EXIT
FI
OD
RETURN (len)
BYTE FUNC GetNumber(CHAR ARRAY s BYTE POINTER pos)
BYTE num,len
CHAR ARRAY tmp(5)
len=0
DO
len==+1
tmp(len)=s(pos^)
pos^==+1
IF s(pos^)<'0 OR s(pos^)>'9 THEN
EXIT
FI
OD
tmp(0)=len
num=ValB(tmp)
RETURN (num)
PROC Append(CHAR ARRAY text,suffix)
BYTE POINTER srcPtr,dstPtr
BYTE len
len=suffix(0)
IF text(0)+len>255 THEN
len=255-text(0)
FI
IF len THEN
srcPtr=suffix+1
dstPtr=text+text(0)+1
MoveBlock(dstPtr,srcPtr,len)
text(0)==+suffix(0)
FI
RETURN
PROC Encode(CHAR ARRAY in,out)
BYTE pos,len
CHAR ARRAY tmp(5)
pos=1 len=0 out(0)=0
WHILE pos<=in(0)
DO
len=GetLength(in,pos)
StrB(len,tmp)
Append(out,tmp)
out(0)==+1
out(out(0))=in(pos)
pos==+len
OD
RETURN
PROC Decode(CHAR ARRAY in,out)
BYTE pos,num,i
CHAR c
pos=1 out(0)=0
WHILE pos<=in(0)
DO
num=GetNumber(in,@pos)
c=in(pos)
pos==+1
FOR i=1 TO num
DO
out(0)==+1
out(out(0))=c
OD
OD
RETURN
PROC Main()
CHAR ARRAY data="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
CHAR ARRAY encoded(256),decoded(256)
PrintE("original:")
PrintE(data)
PutE()
Encode(data,encoded)
PrintE("encoded:")
PrintE(encoded)
PutE()
Decode(encoded,decoded)
PrintE("decoded:")
PrintE(decoded)
RETURN- Output:
Screenshot from Atari 8-bit computer
original: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded: 12W1B12W3B24W1B14W decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Ada
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Fixed; use Ada.Strings.Fixed;
procedure Test_Run_Length_Encoding is
function Encode (Data : String) return String is
begin
if Data'Length = 0 then
return "";
else
declare
Code : constant Character := Data (Data'First);
Index : Integer := Data'First + 1;
begin
while Index <= Data'Last and then Code = Data (Index) loop
Index := Index + 1;
end loop;
declare
Prefix : constant String := Integer'Image (Index - Data'First);
begin
return Prefix (2..Prefix'Last) & Code & Encode (Data (Index..Data'Last));
end;
end;
end if;
end Encode;
function Decode (Data : String) return String is
begin
if Data'Length = 0 then
return "";
else
declare
Index : Integer := Data'First;
Count : Natural := 0;
begin
while Index < Data'Last and then Data (Index) in '0'..'9' loop
Count := Count * 10 + Character'Pos (Data (Index)) - Character'Pos ('0');
Index := Index + 1;
end loop;
if Index > Data'First then
return Count * Data (Index) & Decode (Data (Index + 1..Data'Last));
else
return Data;
end if;
end;
end if;
end Decode;
begin
Put_Line (Encode ("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"));
Put_Line (Decode ("12W1B12W3B24W1B14W"));
end Test_Run_Length_Encoding;
Sample output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
ALGOL 68
Note: The following uses iterators, eliminating the need of declaring arbitrarily large CHAR arrays for caching.
STRING input := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
STRING output := "12W1B12W3B24W1B14W";
MODE YIELDCHAR = PROC(CHAR)VOID;
MODE GENCHAR = PROC(YIELDCHAR)VOID;
PROC gen char string = (REF STRING s, YIELDCHAR yield)VOID:
FOR i FROM LWB s TO UPB s DO yield(s[i]) OD;
CO
# Note: The following 2 lines use currying. This not supported by ELLA ALGOL 68RS #
GENCHAR input seq = gen char string(input,),
output seq = gen char string(output,);
END CO
GENCHAR
input seq = (YIELDCHAR yield)VOID: gen char string(input, yield),
output seq = (YIELDCHAR yield)VOID: gen char string(output, yield);
PROC gen encode = (GENCHAR gen char, YIELDCHAR yield)VOID: (
INT count := 0;
CHAR prev;
# FOR CHAR c IN # gen char( # ) DO ( #
## (CHAR c)VOID: (
IF count = 0 THEN
count := 1;
prev := c
ELIF c NE prev THEN
STRING str count := whole(count,0);
gen char string(str count, yield); count := 1;
yield(prev); prev := c
ELSE
count +:=1
FI
# OD # ));
IF count NE 0 THEN
STRING str count := whole(count,0);
gen char string(str count,yield);
yield(prev)
FI
);
STRING zero2nine = "0123456789";
PROC gen decode = (GENCHAR gen char, YIELDCHAR yield)VOID: (
INT repeat := 0;
# FOR CHAR c IN # gen char( # ) DO ( #
## (CHAR c)VOID: (
IF char in string(c, LOC INT, zero2nine) THEN
repeat := repeat*10 + ABS c - ABS "0"
ELSE
FOR i TO repeat DO yield(c) OD;
repeat := 0
FI
# OD # ))
);
# iterate through input string #
print("Encode input: ");
# FOR CHAR c IN # gen encode(input seq, # ) DO ( #
## (CHAR c)VOID:
print(c)
# OD # );
print(new line);
# iterate through output string #
print("Decode output: ");
# FOR CHAR c IN # gen decode(output seq, # ) DO ( #
## (CHAR c)VOID:
print(c)
# OD # );
print(new line)Output:
Encode input: 12W1B12W3B24W1B14W Decode output: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Amazing Hopper
/*
TASK BASIC-EMBEBIDO de HOPPER
onechar("WB",objetivo)
deja un único carcater de todos los que encuentre consecutivamente,
de la lista de caracteres "WB".
índice:=()
copia el valor de la función entre paréntesis en "índice", pero
deja ese valor en el stack de trabajo, para ser asignado a "largo".
poschar(INICIO, v, objetivo)
entrega la posición donde el caracter dado "v" deja de repetirse
(por eso se resta 1 al resultado).
objetivo+=sublargo
borra los primeros sublargo-ésimo caracteres.
#basic{...} / #(...)
BASIC embebido de Hopper.
*/
#include <basico.h>
#define INICIO 1
#proto codificar(_X_,_Y_,_Z_)
#proto decodificar(_X_,_Y_)
principal {
índice="", largo=0, codificado="", decodificado=""
objetivo = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
decimales '0', fijar separador 'NULO'
#basic{
largo = len(índice:=( onechar("WB",objetivo) ) )
print ("Original =",objetivo,NL)
codificado = codificar(objetivo, índice, largo)
decodificado = decodificar(codificado, índice)
print ("Codificado =",codificado,"\nDecodificado =",decodificado,NL)
}
terminar
}
subrutinas
codificar( o, i, l)
v="", sublargo=0
para cada caracter ( v, i, l )
/* deja ésto en el stack de trabajo: */
#( sublargo := (poschar(INICIO, v, o) - 1 ) ), 'v'
o+=sublargo
siguiente
unir esto
retornar
decodificar(c, i)
v="", posición=0, l=0
#( l=len(i) )
para cada caracter ( v, i, l )
#basic{
posición = find(v, c)-1
/* deja ésto en el stack de trabajo: */
replicate(v, number(copy(posición,1,c)) )
}
++posición,c+=posición
siguiente
unir esto
retornar
- Output:
Original =WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Codificado =12W1B12W3B24W1B14W Decodificado =WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
APL
∇ ret←RLL rll;count
[1] count←∣2-/((1,(2≠/rll),1)×⍳1+⍴rll)~0
[2] ret←(⍕count,¨(1,2≠/rll)/rll)~' '
∇
Sample Output:
RLL 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW' 12W1B12W3B24W1B14W
AppleScript
------------------ RUN-LENGTH ENCODING -----------------
-- encode :: String -> String
on encode(s)
script go
on |λ|(cs)
if {} ≠ cs then
set c to text 1 of cs
set {chunk, residue} to span(eq(c), rest of cs)
(c & (1 + (length of chunk)) as string) & |λ|(residue)
else
""
end if
end |λ|
end script
|λ|(characters of s) of go
end encode
-- decode :: String -> String
on decode(s)
script go
on |λ|(cs)
if {} ≠ cs then
set {ds, residue} to span(my isDigit, rest of cs)
set n to (ds as string) as integer
replicate(n, item 1 of cs) & |λ|(residue)
else
""
end if
end |λ|
end script
|λ|(characters of s) of go
end decode
--------------------------- TEST -------------------------
on run
set src to ¬
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
set encoded to encode(src)
set decoded to decode(encoded)
unlines({encoded, decoded, src = decoded})
end run
-------------------- GENERIC FUNCTIONS -------------------
-- eq :: a -> a -> Bool
on eq(a)
-- True if a and b are equivalent in terms
-- of the AppleScript (=) operator.
script go
on |λ|(b)
a = b
end |λ|
end script
end eq
-- isDigit :: Char -> Bool
on isDigit(c)
set n to (id of c)
48 ≤ n and 57 ≥ n
end isDigit
-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
-- 2nd class handler function lifted into 1st class script wrapper.
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn
-- Egyptian multiplication - progressively doubling a list, appending
-- stages of doubling to an accumulator where needed for binary
-- assembly of a target length
-- replicate :: Int -> String -> String
on replicate(n, s)
-- Egyptian multiplication - progressively doubling a list,
-- appending stages of doubling to an accumulator where needed
-- for binary assembly of a target length
script p
on |λ|({n})
n ≤ 1
end |λ|
end script
script f
on |λ|({n, dbl, out})
if (n mod 2) > 0 then
set d to out & dbl
else
set d to out
end if
{n div 2, dbl & dbl, d}
end |λ|
end script
set xs to |until|(p, f, {n, s, ""})
item 2 of xs & item 3 of xs
end replicate
-- span :: (a -> Bool) -> [a] -> ([a], [a])
on span(p, xs)
-- The longest (possibly empty) prefix of xs
-- that contains only elements satisfying p,
-- tupled with the remainder of xs.
-- span(p, xs) eq (takeWhile(p, xs), dropWhile(p, xs))
script go
property mp : mReturn(p)
on |λ|(vs)
if {} ≠ vs then
set x to item 1 of vs
if |λ|(x) of mp then
set {ys, zs} to |λ|(rest of vs)
{{x} & ys, zs}
else
{{}, vs}
end if
else
{{}, {}}
end if
end |λ|
end script
|λ|(xs) of go
end span
-- unlines :: [String] -> String
on unlines(xs)
-- A single string formed by the intercalation
-- of a list of strings with the newline character.
set {dlm, my text item delimiters} to ¬
{my text item delimiters, linefeed}
set s to xs as text
set my text item delimiters to dlm
s
end unlines
-- until :: (a -> Bool) -> (a -> a) -> a -> a
on |until|(p, f, x)
set v to x
set mp to mReturn(p)
set mf to mReturn(f)
repeat until mp's |λ|(v)
set v to mf's |λ|(v)
end repeat
v
end |until|
- Output:
W12B1W12B3W24B1W14 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW true
Arturo
runlengthEncode: function [s][
join map chunk split s => [&] 'x ->
(to :string size x) ++ first x
]
runlengthDecode: function [s][
result: new ""
loop (chunk split s 'x -> positive? size match x {/\d+/}) [a,b] ->
'result ++ repeat first b to :integer join to [:string] a
return result
]
str: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
encoded: runlengthEncode str
print ["encoded:" encoded]
decoded: runlengthDecode encoded
print ["decoded:" decoded]
if decoded=str -> print "\nSuccess!"
- Output:
encoded: 12W1B12W3B24W1B14W decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Success!
AutoHotkey
MsgBox % key := rle_encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
MsgBox % rle_decode(key)
rle_encode(message)
{
StringLeft, previous, message, 1
StringRight, last, message, 1
message .= Asc(Chr(last)+1)
count = 0
Loop, Parse, message
{
If (previous == A_LoopField)
count +=1
Else
{
output .= previous . count
previous := A_LoopField
count = 1
}
}
Return output
}
rle_decode(message)
{
pos = 1
While, item := RegExMatch(message, "\D", char, pos)
{
digpos := RegExMatch(message, "\d+", dig, item)
Loop, % dig
output .= char
pos := digpos
}
Return output
}
AWK
It works with "textual" input. Lines containing numbers are skipped, since they can't be represented in a not ambiguous way in this implementation (e.g. "11AA" would be encoded as "212A", which would be decoded as A repeated 212 times!)
Encoding
BEGIN {
FS=""
}
/^[^0-9]+$/ {
cp = $1; j = 0
for(i=1; i <= NF; i++) {
if ( $i == cp ) {
j++;
} else {
printf("%d%c", j, cp)
j = 1
}
cp = $i
}
printf("%d%c", j, cp)
}
Decoding
BEGIN {
RS="[0-9]+[^0-9]"
final = "";
}
{
match(RT, /([0-9]+)([^0-9])/, r)
for(i=0; i < int(r[1]); i++) {
final = final r[2]
}
}
END {
print final
}
BaCon
FUNCTION Rle_Encode$(txt$)
LOCAL result$, c$ = LEFT$(txt$, 1)
LOCAL total = 1
FOR x = 2 TO LEN(txt$)
IF c$ = MID$(txt$, x, 1) THEN
INCR total
ELSE
result$ = result$ & STR$(total) & c$
c$ = MID$(txt$, x, 1)
total = 1
END IF
NEXT
RETURN result$ & STR$(total) & c$
END FUNCTION
FUNCTION Rle_Decode$(txt$)
LOCAL nr$, result$
FOR x = 1 TO LEN(txt$)
IF REGEX(MID$(txt$, x, 1), "[[:digit:]]") THEN
nr$ = nr$ & MID$(txt$, x, 1)
ELSE
result$ = result$ & FILL$(VAL(nr$), ASC(MID$(txt$, x, 1)))
nr$ = ""
END IF
NEXT
RETURN result$
END FUNCTION
rle_data$ = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
PRINT "RLEData: ", rle_data$
encoded$ = Rle_Encode$(rle_data$)
PRINT "Encoded: ", encoded$
PRINT "Decoded: ", Rle_Decode$(encoded$)
- Output:
RLEData: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded: 12W1B12W3B24W1B14W Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
BASIC
DECLARE FUNCTION RLDecode$ (i AS STRING)
DECLARE FUNCTION RLEncode$ (i AS STRING)
DIM initial AS STRING, encoded AS STRING, decoded AS STRING
INPUT "Type something: ", initial
encoded = RLEncode(initial)
decoded = RLDecode(encoded)
PRINT initial
PRINT encoded
PRINT decoded
FUNCTION RLDecode$ (i AS STRING)
DIM Loop0 AS LONG, rCount AS STRING, outP AS STRING, m AS STRING
FOR Loop0 = 1 TO LEN(i)
m = MID$(i, Loop0, 1)
SELECT CASE m
CASE "0" TO "9"
rCount = rCount + m
CASE ELSE
IF LEN(rCount) THEN
outP = outP + STRING$(VAL(rCount), m)
rCount = ""
ELSE
outP = outP + m
END IF
END SELECT
NEXT
RLDecode$ = outP
END FUNCTION
FUNCTION RLEncode$ (i AS STRING)
DIM tmp1 AS STRING, tmp2 AS STRING, outP AS STRING
DIM Loop0 AS LONG, rCount AS LONG
tmp1 = MID$(i, 1, 1)
tmp2 = tmp1
rCount = 1
FOR Loop0 = 2 TO LEN(i)
tmp1 = MID$(i, Loop0, 1)
IF tmp1 <> tmp2 THEN
outP = outP + LTRIM$(RTRIM$(STR$(rCount))) + tmp2
tmp2 = tmp1
rCount = 1
ELSE
rCount = rCount + 1
END IF
NEXT
outP = outP + LTRIM$(RTRIM$(STR$(rCount)))
outP = outP + tmp2
RLEncode$ = outP
END FUNCTION
Sample output (last one shows errors from using numbers in input string):
Type something: aaaaeeeeeeiiiioooouuy aaaaeeeeeeiiiioooouuy 4a6e4i4o2u1y aaaaeeeeeeiiiioooouuy Type something: My dog has fleas. My dog has fleas. 1M1y1 1d1o1g1 1h1a1s1 1f1l1e1a1s1. My dog has fleas. Type something: 1r 1r 111r rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
Applesoft BASIC
10 I$ = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
20 GOSUB 100ENCODE
30 GOSUB 200DECODE
40 PRINT "INPUT: ";I$
50 PRINT "OUTPUT: ";
60 GOSUB 250 PRINT
70 END
100 O$ = MID$ (I$,1,1):N$ = MID$ ( CHR$ (0),1, LEN (O$)): IF LEN (I$) < 2 THEN RETURN
110 FOR I = 2 TO LEN (I$):C$ = MID$ (I$,I,1): IF C$ < > RIGHT$ (O$,1) THEN O$ = O$ + C$:N$ = N$ + CHR$ (0): NEXT I: RETURN
120 N$ = MID$ (N$,1, LEN (O$) - 1) + CHR$ ( ASC ( MID$ (N$, LEN (O$))) + 1): NEXT I: RETURN
200 I$ = "": IF LEN (O$) THEN FOR I = 1 TO LEN (O$): FOR J = 0 TO ASC ( MID$ (N$,I)):I$ = I$ + MID$ (O$,I,1): NEXT J,I
210 RETURN
250 IF LEN (O$) THEN FOR I = 1 TO LEN (O$): PRINT ASC ( MID$ (N$,I)) + 1; MID$ (O$,I,1);: NEXT I
260 RETURN
- Output:
INPUT: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW OUTPUT: 12W1B12W3B24W1B14W
BASIC256
function FBString(lon, cad$)
# Definimos la función String en BASIC256
cadena$ = ""
for a = 1 to lon
cadena$ += cad$
next a
return cadena$
end function
function RLDecode(i$)
rCount$ = "" : outP$ = ""
for Loop0 = 1 to length(i$)
m$ = mid(i$, Loop0, 1)
begin case
case m$ = "0"
rCount$ += m$
case m$ = "1"
rCount$ += m$
case m$ = "2"
rCount$ += m$
case m$ = "3"
rCount$ += m$
case m$ = "4"
rCount$ += m$
case m$ = "5"
rCount$ += m$
case m$ = "6"
rCount$ += m$
case m$ = "7"
rCount$ += m$
case m$ = "8"
rCount$ += m$
case m$ = "9"
rCount$ += m$
else
if length(rCount$) then
outP$ += FBString(int(rCount$), m$)
rCount$ = ""
else
outP$ += m$
end if
end case
next Loop0
RLDecode = outP$
end function
function RLEncode(i$)
outP$ = ""
tmp1 = mid(i$, 1, 1)
tmp2 = tmp1
rCount = 1
for Loop0 = 2 to length(i$)
tmp1 = mid(i$, Loop0, 1)
if tmp1 <> tmp2 then
outP$ += string(rCount) + tmp2
tmp2 = tmp1
rCount = 1
else
rCount += 1
end if
next Loop0
outP$ += replace(string(rCount)," ", "")
outP$ += tmp2
RLEncode = outP$
end function
input "Type something: ", initial
encoded$ = RLEncode(initial)
decoded$ = RLDecode(encoded$)
print initial
print encoded$
print decoded$
end- Output:
La salida es similar a la de BASIC, mostrada arriba.
BBC BASIC
The run counts are indicated by means of character codes in the range 131 to 255.
input$ = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
PRINT "Input: " input$
rle$ = FNencodeRLE(input$)
output$ = FNdecodeRLE(rle$)
PRINT "Output: " output$
END
DEF FNencodeRLE(text$)
LOCAL n%, r%, c$, o$
n% = 1
WHILE n% <= LEN(text$)
c$ = MID$(text$, n%, 1)
n% += 1
r% = 1
WHILE c$ = MID$(text$, n%, 1) AND r% < 127
r% += 1
n% += 1
ENDWHILE
IF r% < 3 o$ += STRING$(r%, c$) ELSE o$ += CHR$(128+r%) + c$
ENDWHILE
= o$
DEF FNdecodeRLE(rle$)
LOCAL n%, c$, o$
n% = 1
WHILE n% <= LEN(rle$)
c$ = MID$(rle$, n%, 1)
n% += 1
IF ASC(c$) > 128 THEN
o$ += STRING$(ASC(c$)-128, MID$(rle$, n%, 1))
n% += 1
ELSE
o$ += c$
ENDIF
ENDWHILE
= o$
Befunge
Not the same format as in the example,it puts "n\n" at the beginning so you can pipe the output back in and receive the input. Pipe the output of the program-it's more reliable.
~"y"- ~$ v
<temp var for when char changes
format:
first,'n' and a newline. :
a char then a v _"n",v
number then a space continuously 9
example: 1
n > v ,+<
a5 b2
decoded:aaaaabb
the program is ended using decoder
Ctrl-C on linux,or alt-f4
on windows.copy the output >\v encoder
of the program somewhere ^_ $ v
to encode press y : > $11g:, v
to decode pipe file in >1-^ ~ v +1\<
the output of the encoder \ v< $ ^ .\_^
starts with n,this is so ^,:<\&~< _~:,>1>\:v>^
you can pipe it straight in ^ <
~
the spaces seem to be a annoying thing :
thanks to CCBI...if a interpreter dosen't 1
create them it's non-conforming and thus 1
the validity of this program is NOT affected p-
>^
--written by Gamemanj,for Rosettacode
Bracmat
( run-length
= character otherCharacter acc begin end
. :?acc
& 0:?begin
& @( !arg
: ?
[!begin
%@?character
?
[?end
( (%@:~!character:?otherCharacter) ?
& !acc !end+-1*!begin !character:?acc
& !otherCharacter:?character
& !end:?begin
& ~`
| &!acc !end+-1*!begin !character:?acc
)
)
& str$!acc
)
& run-length$WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW12W1B12W3B24W1B14W
Burlesque
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
=[{^^[~\/L[Sh}\mC
Encoder that can deal with byte streams. Can encode/decode any byte values and any length with reasonable efficiency. Also showing OO and polymophism with structs.
#include <stdio.h>
#include <stdlib.h>
typedef struct stream_t stream_t, *stream;
struct stream_t {
/* get function is supposed to return a byte value (0-255),
or -1 to signify end of input */
int (*get)(stream);
/* put function does output, one byte at a time */
int (*put)(stream, int);
};
/* next two structs inherit from stream_t */
typedef struct {
int (*get)(stream);
int (*put)(stream, int);
char *string;
int pos;
} string_stream;
typedef struct {
int (*get)(stream);
int (*put)(stream, int);
FILE *fp;
} file_stream;
/* methods for above streams */
int sget(stream in)
{
int c;
string_stream* s = (string_stream*) in;
c = (unsigned char)(s->string[s->pos]);
if (c == '\0') return -1;
s->pos++;
return c;
}
int sput(stream out, int c)
{
string_stream* s = (string_stream*) out;
s->string[s->pos++] = (c == -1) ? '\0' : c;
if (c == -1) s->pos = 0;
return 0;
}
int file_put(stream out, int c)
{
file_stream *f = (file_stream*) out;
return fputc(c, f->fp);
}
/* helper function */
void output(stream out, unsigned char* buf, int len)
{
int i;
out->put(out, 128 + len);
for (i = 0; i < len; i++)
out->put(out, buf[i]);
}
/* Specification: encoded stream are unsigned bytes consisting of sequences.
* First byte of each sequence is the length, followed by a number of bytes.
* If length <=128, the next byte is to be repeated length times;
* If length > 128, the next (length - 128) bytes are not repeated.
* this is to improve efficiency for long non-repeating sequences.
* This scheme can encode arbitrary byte values efficiently.
* c.f. Adobe PDF spec RLE stream encoding (not exactly the same)
*/
void encode(stream in, stream out)
{
unsigned char buf[256];
int len = 0, repeat = 0, end = 0, c;
int (*get)(stream) = in->get;
int (*put)(stream, int) = out->put;
while (!end) {
end = ((c = get(in)) == -1);
if (!end) {
buf[len++] = c;
if (len <= 1) continue;
}
if (repeat) {
if (buf[len - 1] != buf[len - 2])
repeat = 0;
if (!repeat || len == 129 || end) {
/* write out repeating bytes */
put(out, end ? len : len - 1);
put(out, buf[0]);
buf[0] = buf[len - 1];
len = 1;
}
} else {
if (buf[len - 1] == buf[len - 2]) {
repeat = 1;
if (len > 2) {
output(out, buf, len - 2);
buf[0] = buf[1] = buf[len - 1];
len = 2;
}
continue;
}
if (len == 128 || end) {
output(out, buf, len);
len = 0;
repeat = 0;
}
}
}
put(out, -1);
}
void decode(stream in, stream out)
{
int c, i, cnt;
while (1) {
c = in->get(in);
if (c == -1) return;
if (c > 128) {
cnt = c - 128;
for (i = 0; i < cnt; i++)
out->put(out, in->get(in));
} else {
cnt = c;
c = in->get(in);
for (i = 0; i < cnt; i++)
out->put(out, c);
}
}
}
int main()
{
char buf[256];
string_stream str_in = { sget, 0,
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW", 0};
string_stream str_out = { sget, sput, buf, 0 };
file_stream file = { 0, file_put, stdout };
/* encode from str_in to str_out */
encode((stream)&str_in, (stream)&str_out);
/* decode from str_out to file (stdout) */
decode((stream)&str_out, (stream)&file);
return 0;
}
C#
Linq
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Linq.Enumerable;
namespace RunLengthEncoding
{
static class Program
{
public static string Encode(string input) => input.Length ==0 ? "" : input.Skip(1)
.Aggregate((t:input[0].ToString(),o:Empty<string>()),
(a,c)=>a.t[0]==c ? (a.t+c,a.o) : (c.ToString(),a.o.Append(a.t)),
a=>a.o.Append(a.t).Select(p => (key: p.Length, chr: p[0])))
.Select(p=> $"{p.key}{p.chr}")
.StringConcat();
public static string Decode(string input) => input
.Aggregate((t: "", o: Empty<string>()), (a, c) => !char.IsDigit(c) ? ("", a.o.Append(a.t+c)) : (a.t + c,a.o)).o
.Select(p => new string(p.Last(), int.Parse(string.Concat(p.Where(char.IsDigit)))))
.StringConcat();
private static string StringConcat(this IEnumerable<string> seq) => string.Concat(seq);
public static void Main(string[] args)
{
const string raw = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
const string encoded = "12W1B12W3B24W1B14W";
WriteLine($"raw = {raw}");
WriteLine($"encoded = {encoded}");
WriteLine($"Encode(raw) = encoded = {Encode(raw)}");
WriteLine($"Decode(encode) = {Decode(encoded)}");
WriteLine($"Decode(Encode(raw)) = {Decode(Encode(raw)) == raw}");
ReadLine();
}
}
}
Output:
raw = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded = 12W1B12W3B24W1B14W Encode(raw) = encoded = 12W1B12W3B24W1B14W Decode(encode) = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Decode(Encode(raw)) = True
Many solutions do not follow the suggested output guideline in the challenge (not helped by its wording), instead producing a list of tuples or equivalent. This is much simpler (especially for decode) and the following provides an equivalent of those (IMHO deficient) solutions, to make comparisons easier.
using System.Collections.Generic;
using System.Linq;
using static System.Console;
namespace RunLengthEncoding
{
static class Program
{
public static string Encode(string input) => input.Length ==0 ? "" : input.Skip(1)
.Aggregate((t:input[0].ToString(),o:Empty<string>()),
(a,c)=>a.t[0]==c ? (a.t+c,a.o) : (c.ToString(),a.o.Append(a.t)),
a=>a.o.Append(a.t).Select(p => (key: p.Length, chr: p[0])));
public static string Decode(IEnumerable<(int i , char c)> input) =>
string.Concat(input.Select(t => new string(t.c, t.i)));
public static void Main(string[] args)
{
const string raw = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
var encoded = new[] { (12, 'W'), (1, 'B'), (12, 'W'), (3, 'B'), (24, 'W'), (1, 'B'), (14, 'W') };
WriteLine($"raw = {raw}");
WriteLine($"Encode(raw) = encoded = {Encode(raw).TupleListToString()}");
WriteLine($"Decode(encoded) = {Decode(encoded)}");
WriteLine($"Decode(Encode(raw)) = {Decode(Encode(raw)) == raw}");
ReadLine();
}
private static string TupleListToString(this IEnumerable<(int i, char c)> list) =>
string.Join(",", list.Select(t => $"[{t.i},{t.c}]"));
}
}
Output:
raw = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encode(raw) = encoded = [12,W],[1,B],[12,W],[3,B],[24,W],[1,B],[14,W] Decode(encoded) = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Decode(Encode(raw)) = True
Stringbuilder version. Might be more performant but mixes output formatting with encoding/decoding logic.
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Text;
namespace RunLengthEncoding
{
static class Program
{
public static string Encode(string input) => input.Length == 0 ? "" : input.Skip(1)
.Aggregate((len: 1, chr: input[0], sb: new StringBuilder()),
(a, c) => a.chr == c ? (a.len + 1, a.chr, a.sb)
: (1, c, a.sb.Append(a.len).Append(a.chr))),
a => a.sb.Append(a.len).Append(a.chr)))
.ToString();
public static string Decode(string input) => input
.Aggregate((t: "", sb: new StringBuilder()),
(a, c) => !char.IsDigit(c) ? ("", a.sb.Append(new string(c, int.Parse(a.t))))
: (a.t + c, a.sb))
.sb.ToString();
public static void Main(string[] args)
{
const string raw = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
const string encoded = "12W1B12W3B24W1B14W";
WriteLine($"raw = {raw}");
WriteLine($"encoded = {encoded}");
WriteLine($"Encode(raw) = encoded = {Encode(raw)}");
WriteLine($"Decode(encode) = {Decode(encoded)}");
WriteLine($"Decode(Encode(raw)) = {Decode(Encode(raw)) == raw}");
ReadLine();
}
}
}
Output:
raw = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded = 12W1B12W3B24W1B14W Encode(raw) = encoded = 12W1B12W3B24W1B14W Decode(encode) = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Decode(Encode(raw)) = True
Imperative
This example only works if there are no digits in the string to be encoded and then decoded.
public static void Main(string[] args)
{
string input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
Console.WriteLine(Encode(input));//Outputs: 12W1B12W3B24W1B14W
Console.WriteLine(Decode(Encode(input)));//Outputs: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Console.ReadLine();
}
public static string Encode(string s)
{
StringBuilder sb = new StringBuilder();
int count = 1;
char current =s[0];
for(int i = 1; i < s.Length;i++)
{
if (current == s[i])
{
count++;
}
else
{
sb.AppendFormat("{0}{1}", count, current);
count = 1;
current = s[i];
}
}
sb.AppendFormat("{0}{1}", count, current);
return sb.ToString();
}
public static string Decode(string s)
{
string a = "";
int count = 0;
StringBuilder sb = new StringBuilder();
char current = char.MinValue;
for(int i = 0; i < s.Length; i++)
{
current = s[i];
if (char.IsDigit(current))
a += current;
else
{
count = int.Parse(a);
a = "";
for (int j = 0; j < count; j++)
sb.Append(current);
}
}
return sb.ToString();
}
RegEx
Somewhat shorter, using Regex.Replace with MatchEvaluator (using C#2 syntax only):
using System;
using System.Text.RegularExpressions;
public class Program
{
private delegate void fOk(bool ok, string message);
public static int Main(string[] args)
{
const string raw = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
const string code = "12W1B12W3B24W1B14W";
fOk Ok = delegate(bool ok, string message)
{
Console.WriteLine("{0}: {1}", ok ? "ok" : "not ok", message);
};
Ok(code.Equals(Encode(raw)), "Encode");
Ok(raw.Equals(Decode(code)), "Decode");
return 0;
}
public static string Encode(string input)
{
return Regex.Replace(input, @"(.)\1*", delegate(Match m)
{
return string.Concat(m.Value.Length, m.Groups[1].Value);
});
}
public static string Decode(string input)
{
return Regex.Replace(input, @"(\d+)(\D)", delegate(Match m)
{
return new string(m.Groups[2].Value[0], int.Parse(m.Groups[1].Value));
});
}
}
C++
#include <algorithm>
#include <array>
#include <iterator>
#include <limits>
#include <tuple>
namespace detail_ {
// For constexpr digit<->number conversions.
constexpr auto digits = std::array{'0','1','2','3','4','5','6','7','8','9'};
// Helper function to encode a run-length.
template <typename OutputIterator>
constexpr auto encode_run_length(std::size_t n, OutputIterator out)
{
constexpr auto base = digits.size();
// Determine the number of digits needed.
auto const num_digits = [base](auto n)
{
auto d = std::size_t{1};
while ((n /= digits.size()))
++d;
return d;
}(n);
// Helper lambda to raise the base to an integer power.
auto base_power = [base](auto n)
{
auto res = decltype(base){1};
for (auto i = decltype(n){1}; i < n; ++i)
res *= base;
return res;
};
// From the most significant digit to the least, output the digit.
for (auto i = decltype(num_digits){0}; i < num_digits; ++i)
*out++ = digits[(n / base_power(num_digits - i)) % base];
return out;
}
// Helper function to decode a run-length.
// As of C++20, this can be constexpr, because std::find() is constexpr.
// Before C++20, it can be constexpr by emulating std::find().
template <typename InputIterator>
auto decode_run_length(InputIterator first, InputIterator last)
{
auto count = std::size_t{0};
while (first != last)
{
// If the next input character is not a digit, we're done.
auto const p = std::find(digits.begin(), digits.end(), *first);
if (p == digits.end())
break;
// Convert the digit to a number, and append it to the size.
count *= digits.size();
count += std::distance(digits.begin(), p);
// Move on to the next input character.
++first;
}
return std::tuple{count, first};
}
} // namespace detail_
template <typename InputIterator, typename OutputIterator>
constexpr auto encode(InputIterator first, InputIterator last, OutputIterator out)
{
while (first != last)
{
// Read the next value.
auto const value = *first++;
// Increase the count as long as the next value is the same.
auto count = std::size_t{1};
while (first != last && *first == value)
{
++count;
++first;
}
// Write the value and its run length.
out = detail_::encode_run_length(count, out);
*out++ = value;
}
return out;
}
// As of C++20, this can be constexpr, because std::find() and
// std::fill_n() are constexpr (and decode_run_length() can be
// constexpr, too).
// Before C++20, it can be constexpr by emulating std::find() and
// std::fill_n().
template <typename InputIterator, typename OutputIterator>
auto decode(InputIterator first, InputIterator last, OutputIterator out)
{
while (first != last)
{
using detail_::digits;
// Assume a run-length of 1, then try to decode the actual
// run-length, if any.
auto count = std::size_t{1};
if (std::find(digits.begin(), digits.end(), *first) != digits.end())
std::tie(count, first) = detail_::decode_run_length(first, last);
// Write the run.
out = std::fill_n(out, count, *first++);
}
return out;
}
template <typename Range, typename OutputIterator>
constexpr auto encode(Range&& range, OutputIterator out)
{
using std::begin;
using std::end;
return encode(begin(range), end(range), out);
}
template <typename Range, typename OutputIterator>
auto decode(Range&& range, OutputIterator out)
{
using std::begin;
using std::end;
return decode(begin(range), end(range), out);
}
// Sample application and checking ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <iostream>
#include <string_view>
int main()
{
using namespace std::literals;
constexpr auto test_string = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"sv;
std::cout << "Input: \"" << test_string << "\"\n";
std::cout << "Output: \"";
// No need for a temporary string - can encode directly to cout.
encode(test_string, std::ostreambuf_iterator<char>{std::cout});
std::cout << "\"\n";
auto encoded_str = std::string{};
auto decoded_str = std::string{};
encode(test_string, std::back_inserter(encoded_str));
decode(encoded_str, std::back_inserter(decoded_str));
std::cout.setf(std::cout.boolalpha);
std::cout << "Round trip works: " << (test_string == decoded_str) << '\n';
}
#include <iostream>
#include <string>
#include <sstream>
#include <boost/regex.hpp>
#include <cstdlib>
std::string encode ( const std::string & ) ;
std::string decode ( const std::string & ) ;
int main( ) {
std::string to_encode ( "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" ) ;
std::cout << to_encode << " encoded:" << std::endl ;
std::string encoded ( encode ( to_encode ) ) ;
std::cout << encoded << std::endl ;
std::string decoded ( decode( encoded ) ) ;
std::cout << "Decoded again:\n" ;
std::cout << decoded << std::endl ;
if ( to_encode == decoded )
std::cout << "It must have worked!\n" ;
return 0 ;
}
std::string encode( const std::string & to_encode ) {
std::string::size_type found = 0 , nextfound = 0 ;
std::ostringstream oss ;
nextfound = to_encode.find_first_not_of( to_encode[ found ] , found ) ;
while ( nextfound != std::string::npos ) {
oss << nextfound - found ;
oss << to_encode[ found ] ;
found = nextfound ;
nextfound = to_encode.find_first_not_of( to_encode[ found ] , found ) ;
}
//since we must not discard the last characters we add them at the end of the string
std::string rest ( to_encode.substr( found ) ) ;//last run of characters starts at position found
oss << rest.length( ) << to_encode[ found ] ;
return oss.str( ) ;
}
std::string decode ( const std::string & to_decode ) {
boost::regex e ( "(\\d+)(\\w)" ) ;
boost::match_results<std::string::const_iterator> matches ;
std::ostringstream oss ;
std::string::const_iterator start = to_decode.begin( ) , end = to_decode.end( ) ;
while ( boost::regex_search ( start , end , matches , e ) ) {
std::string numberstring ( matches[ 1 ].first , matches[ 1 ].second ) ;
int number = atoi( numberstring.c_str( ) ) ;
std::string character ( matches[ 2 ].first , matches[ 2 ].second ) ;
for ( int i = 0 ; i < number ; i++ )
oss << character ;
start = matches[ 2 ].second ;
}
return oss.str( ) ;
}
Ceylon
shared void run() {
"Takes a string such as aaaabbbbbbcc and returns 4a6b2c"
String compress(String string) {
if (exists firstChar = string.first) {
if (exists index = string.firstIndexWhere((char) => char != firstChar)) {
return "``index````firstChar````compress(string[index...])``";
}
else {
return "``string.size````firstChar``";
}
}
else {
return "";
}
}
"Takes a string such as 4a6b2c and returns aaaabbbbbbcc"
String decompress(String string) =>
let (runs = string.split(Character.letter, false).paired)
"".join {
for ([length, char] in runs)
if (is Integer int = Integer.parse(length))
char.repeat(int)
};
assert (compress("aaaabbbbbaa") == "4a5b2a");
assert (decompress("4a6b2c") == "aaaabbbbbbcc");
assert (compress("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW") == "12W1B12W3B24W1B14W");
assert (decompress("24a") == "aaaaaaaaaaaaaaaaaaaaaaaa");
}
Clojure
(defn compress [s]
(->> (partition-by identity s) (mapcat (juxt count first)) (apply str)))
(defn extract [s]
(->> (re-seq #"(\d+)([A-Z])" s)
(mapcat (fn [[_ n ch]] (repeat (Integer/parseInt n) ch)))
(apply str)))
COBOL
>>SOURCE FREE
IDENTIFICATION DIVISION.
PROGRAM-ID. run-length-encoding.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
FUNCTION encode
FUNCTION decode
.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 input-str PIC A(100).
01 encoded PIC X(200).
01 decoded PIC X(200).
PROCEDURE DIVISION.
ACCEPT input-str
MOVE encode(FUNCTION TRIM(input-str)) TO encoded
DISPLAY "Encoded: " FUNCTION TRIM(encoded)
DISPLAY "Decoded: " FUNCTION TRIM(decode(encoded))
.
END PROGRAM run-length-encoding.
IDENTIFICATION DIVISION.
FUNCTION-ID. encode.
DATA DIVISION.
LOCAL-STORAGE SECTION.
01 str-len PIC 9(3) COMP.
01 i PIC 9(3) COMP.
01 current-char PIC A.
01 num-chars PIC 9(3) COMP.
01 num-chars-disp PIC Z(3).
01 encoded-pos PIC 9(3) COMP VALUE 1.
LINKAGE SECTION.
01 str PIC X ANY LENGTH.
01 encoded PIC X(200).
PROCEDURE DIVISION USING str RETURNING encoded.
MOVE FUNCTION LENGTH(str) TO str-len
MOVE str (1:1) TO current-char
MOVE 1 TO num-chars
PERFORM VARYING i FROM 2 BY 1 UNTIL i > str-len
IF str (i:1) <> current-char
CALL "add-num-chars" USING encoded, encoded-pos,
CONTENT current-char, num-chars
MOVE str (i:1) TO current-char
MOVE 1 TO num-chars
ELSE
ADD 1 TO num-chars
END-IF
END-PERFORM
CALL "add-num-chars" USING encoded, encoded-pos, CONTENT current-char,
num-chars
.
END FUNCTION encode.
IDENTIFICATION DIVISION.
PROGRAM-ID. add-num-chars.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 num-chars-disp PIC Z(3).
LINKAGE SECTION.
01 str PIC X(200).
01 current-pos PIC 9(3) COMP.
01 char-to-encode PIC X.
01 num-chars PIC 9(3) COMP.
PROCEDURE DIVISION USING str, current-pos, char-to-encode, num-chars.
MOVE num-chars TO num-chars-disp
MOVE FUNCTION TRIM(num-chars-disp) TO str (current-pos:3)
ADD FUNCTION LENGTH(FUNCTION TRIM(num-chars-disp)) TO current-pos
MOVE char-to-encode TO str (current-pos:1)
ADD 1 TO current-pos
.
END PROGRAM add-num-chars.
IDENTIFICATION DIVISION.
FUNCTION-ID. decode.
DATA DIVISION.
LOCAL-STORAGE SECTION.
01 encoded-pos PIC 9(3) COMP VALUE 1.
01 decoded-pos PIC 9(3) COMP VALUE 1.
01 num-of-char PIC 9(3) COMP VALUE 0.
LINKAGE SECTION.
01 encoded PIC X(200).
01 decoded PIC X(100).
PROCEDURE DIVISION USING encoded RETURNING decoded.
PERFORM VARYING encoded-pos FROM 1 BY 1
UNTIL encoded (encoded-pos:2) = SPACES OR encoded-pos > 200
IF encoded (encoded-pos:1) IS NUMERIC
COMPUTE num-of-char = num-of-char * 10
+ FUNCTION NUMVAL(encoded (encoded-pos:1))
ELSE
PERFORM UNTIL num-of-char = 0
MOVE encoded (encoded-pos:1) TO decoded (decoded-pos:1)
ADD 1 TO decoded-pos
SUBTRACT 1 FROM num-of-char
END-PERFORM
END-IF
END-PERFORM
.
END FUNCTION decode.
- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded: 12W1B12W3B24W1B14W Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
CoffeeScript
encode = (str) ->
str.replace /(.)\1*/g, (w) ->
w[0] + w.length
decode = (str) ->
str.replace /(.)(\d+)/g, (m,w,n) ->
new Array(+n+1).join(w)
console.log s = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
console.log encode s
console.log decode encode s
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW W12B1W12B3W24B1W14 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
The following version encodes the number of ocurrences as an unicode character. You can change the way it looks by rotating the offset.
encode = (str, offset = 75) ->
str.replace /(.)\1*/g, (w) ->
w[0] + String.fromCharCode(offset+w.length)
decode = (str, offset = 75) ->
str.split('').map((w,i) ->
if not (i%2) then w else new Array(+w.charCodeAt(0)-offset).join(str[i-1])
).join('')
> encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" WWBLWWBNWcBLWY > encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW", 1200 WҼBұWҼBҳWӈBұWҾ > encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW", 5200 WᑜBᑑWᑜBᑓWᑨBᑑWᑞ
Common Lisp
(defun group-similar (sequence &key (test 'eql))
(loop for x in (rest sequence)
with temp = (subseq sequence 0 1)
if (funcall test (first temp) x)
do (push x temp)
else
collect temp
and do (setf temp (list x))))
(defun run-length-encode (sequence)
(mapcar (lambda (group) (list (first group) (length group)))
(group-similar (coerce sequence 'list))))
(defun run-length-decode (sequence)
(reduce (lambda (s1 s2) (concatenate 'simple-string s1 s2))
(mapcar (lambda (elem)
(make-string (second elem)
:initial-element
(first elem)))
sequence)))
(run-length-encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
(run-length-decode '((#\W 12) (#\B 1) (#\W 12) (#\B 3) (#\W 24) (#\B 1)))
D
Short Functional Version
import std.algorithm, std.array;
alias encode = group;
auto decode(Group!("a == b", string) enc) {
return enc.map!(t => [t[0]].replicate(t[1])).join;
}
void main() {
immutable s = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWW" ~
"WWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
assert(s.encode.decode.equal(s));
}
Basic Imperative Version
import std.stdio, std.array, std.conv;
// Similar to the 'look and say' function.
string encode(in string input) pure nothrow @safe {
if (input.empty)
return input;
char last = input[$ - 1];
string output;
int count;
foreach_reverse (immutable c; input) {
if (c == last) {
count++;
} else {
output = count.text ~ last ~ output;
count = 1;
last = c;
}
}
return count.text ~ last ~ output;
}
string decode(in string input) pure /*@safe*/ {
string i, result;
foreach (immutable c; input)
switch (c) {
case '0': .. case '9':
i ~= c;
break;
case 'A': .. case 'Z':
if (i.empty)
throw new Exception("Can not repeat a letter " ~
"without a number of repetitions");
result ~= [c].replicate(i.to!int);
i.length = 0;
break;
default:
throw new Exception("'" ~ c ~ "' is not alphanumeric");
}
return result;
}
void main() {
immutable txt = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWW" ~
"WWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
writeln("Input: ", txt);
immutable encoded = txt.encode;
writeln("Encoded: ", encoded);
assert(txt == encoded.decode);
}
- Output:
Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded: 12W1B12W3B24W1B14W
UTF String Version
D's native string is utf-encoded. This version works for utf string, and uses a Variable-length Quantity module.
import std.stdio, std.conv, std.utf, std.array;
import vlq;
struct RLE { // for utf string
ubyte[] encoded;
RLE encode(const string s) {
validate(s); // check if s is well-formed utf, throw if not
encoded.length = 0; // reset
if (s.length == 0) return this; // empty string
string last;
VLQ count;
for (int i = 0; i < s.length; ) {
auto k = s.stride(i);
auto ucode = cast(string)s[i .. i + k];
if (i == 0) last = ucode;
if (ucode == last)
count++;
else {
encoded ~= count.toVLQ ~ cast(ubyte[])last;
last = ucode;
count = 1;
}
i += k;
}
encoded ~= VLQ(count).toVLQ ~ cast(ubyte[])last;
return this;
}
int opApply(int delegate(ref ulong c, ref string u) dg) {
VLQ count;
string ucode;
for (int i = 0; i < encoded.length; ) {
auto k = count.extract(encoded[i .. $]);
i += k;
if (i >= encoded.length)
throw new Exception("not valid encoded string");
k = stride(cast(string) encoded[i .. $], 0);
if (k == 0xff) // not valid utf code point
throw new Exception("not valid encoded string");
ucode = cast(string)encoded[i .. i + k].dup;
dg(count.value, ucode);
i += k;
}
return 0;
}
string toString() {
string res;
foreach (ref i, s ; this)
if (indexOf("0123456789#", s) == -1)
res ~= text(i) ~ s;
else
res ~= text(i) ~ '#' ~ s;
return res;
}
string decode() {
string res;
foreach (ref i, s; this)
res ~= replicate(s, cast(uint)i);
return res;
}
}
void main() {
RLE r;
auto s = "尋尋覓覓冷冷清清淒淒慘慘戚戚\nWWWWWWWWWWWWBWWWWWWWWWWW" ~
"WBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW\n" ~
"11#222##333";
auto f = File("display.txt", "w");
f.writeln(s);
r.encode(s);
f.writefln("-----\n%s\n-----\n%s", r, r.decode());
auto sEncoded = RLE.init.encode(s).encoded ;
assert(s == RLE(sEncoded).decode(), "Not work");
}
output from "display.txt":
尋尋覓覓冷冷清清淒淒慘慘戚戚 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 11#222##333 ----- 2尋2覓2冷2清2淒2慘2戚1 12W1B12W3B24W1B14W1 2#11##3#22##3#3 ----- 尋尋覓覓冷冷清清淒淒慘慘戚戚 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 11#222##333
NOTE: some characters in this section use Chinese font.
UTF String Version with Regular Expression
The code looks more complex than the third Python version because this also handles digits by escaping them with #.
import std.stdio, std.conv, std.array, std.regex, std.utf,
std.algorithm;
string reEncode(string s) {
validate(s); // Throw if it's not a well-formed UTF string
static string rep(Captures!string m) {
auto c = canFind("0123456789#", m[1]) ? "#" ~ m[1] : m[1];
return text(m.hit.length / m[1].length) ~ c;
}
return std.regex.replace!rep(s, regex(`(.|[\n\r\f])\1*`, "g"));
}
string reDecode(string s) {
validate(s); // Throw if it's not a well-formed UTF string
static string rep(Captures!string m) {
string c = m[2];
if (c.length > 1 && c[0] == '#')
c = c[1 .. $];
return replicate(c, to!int(m[1]));
}
auto r=regex(`(\d+)(#[0123456789#]|[\n\r\f]|[^0123456789#\n\r\f]+)`
, "g");
return std.regex.replace!rep(s, r);
}
void main() {
auto s = "尋尋覓覓冷冷清清淒淒慘慘戚戚\nWWWWWWWWWWWWBWWWWWWWWWWW" ~
"WBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW\n" ~
"11#222##333";
assert(s == reDecode(reEncode(s)));
}
Déjà Vu
rle:
if not dup:
drop
return []
swap ]
local :source chars
pop-from source
1
for c in source:
if = c over:
++
else:
1 c &
&
return [
rld:
)
for pair in swap:
repeat &< pair:
&> pair
concat(
rle "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
!. dup
!. rld- Output:
[ & 12 "W" & 1 "B" & 12 "W" & 3 "B" & 24 "W" & 1 "B" & 14 "W" ] "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Delphi
program RunLengthTest;
{$APPTYPE CONSOLE}
uses
System.SysUtils;
type
TRLEPair = record
count: Integer;
letter: Char;
end;
TRLEncoded = TArray<TRLEPair>;
TRLEncodedHelper = record helper for TRLEncoded
public
procedure Clear;
function Add(c: Char): Integer;
procedure Encode(Data: string);
function Decode: string;
function ToString: string;
end;
{ TRLEncodedHelper }
function TRLEncodedHelper.Add(c: Char): Integer;
begin
SetLength(self, length(self) + 1);
Result := length(self) - 1;
with self[Result] do
begin
count := 1;
letter := c;
end;
end;
procedure TRLEncodedHelper.Clear;
begin
SetLength(self, 0);
end;
function TRLEncodedHelper.Decode: string;
var
p: TRLEPair;
begin
Result := '';
for p in Self do
Result := Result + string.Create(p.letter, p.count);
end;
procedure TRLEncodedHelper.Encode(Data: string);
var
pivot: Char;
i, index: Integer;
begin
Clear;
if Data.Length = 0 then
exit;
pivot := Data[1];
index := Add(pivot);
for i := 2 to Data.Length do
begin
if pivot = Data[i] then
inc(self[index].count)
else
begin
pivot := Data[i];
index := Add(pivot);
end;
end;
end;
function TRLEncodedHelper.ToString: string;
var
p: TRLEPair;
begin
Result := '';
for p in Self do
Result := Result + p.count.ToString + p.letter;
end;
const
Input = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW';
var
Data: TRLEncoded;
begin
Data.Encode(Input);
Writeln(Data.ToString);
writeln(Data.Decode);
Readln;
end.
- Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
DuckDB
In this section, we first show that the SQL presented at #SQL on this page runs properly using DuckDB. We then define a DuckDB function that performs the encoding; apart from illustrating DuckDB's support for functional abstraction, this definition may be of interest as it is significantly shorter and simpler than the corresponding implementation in the SQL section, and would appear to be far more efficient, e.g. because no partitioning is involved.
Compatibility with pgSQL
Here's a transcript showing the output generated using the SQL presented at #SQL on this page.
D .read run-length-encoding-part1.sql ┌─────────────────────────────────────────────────────────────────────┬────────────────────┐ │ plain_text │ Rle_Compressed │ │ varchar │ varchar │ ├─────────────────────────────────────────────────────────────────────┼────────────────────┤ │ WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW │ 12W1B12W3B24W1B14W │ └─────────────────────────────────────────────────────────────────────┴────────────────────┘ D .read run-length-encoding-sql-part2.sql ┌──────────────┬───────────────────────┐ │ rle_encoded │ decoded_string │ │ varchar │ varchar │ ├──────────────┼───────────────────────┤ │ 1A2B3C4D5E6F │ ABBCCCDDDDEEEEEFFFFFF │ └──────────────┴───────────────────────┘
DuckDB function: run_length_encode(s)
create or replace function run_length_encode(str) as table
(WITH RECURSIVE cte AS (
SELECT
1 AS pos,
1 AS counter,
SUBSTRING(str, 1, 1) AS char,
SUBSTRING(str, 2, 1) AS nextc,
UNION ALL
SELECT
pos + 1 as pos,
CASE
WHEN nextc = char THEN counter + 1
ELSE 1
END as counter,
nextc as char,
SUBSTRING(str, 2 + pos, 1) as nextc
FROM cte
WHERE pos < LENGTH(str)
)
SELECT STRING_AGG( counter || char, '' ) AS encoded_string
FROM cte
WHERE nextc != char
);
Example:
from run_length_encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW');
- Output:
┌────────────────────┐ │ encoded_string │ │ varchar │ ├────────────────────┤ │ 12W1B12W3B24W1B14W │ └────────────────────┘
E
def rle(string) {
var seen := null
var count := 0
var result := []
def put() {
if (seen != null) {
result with= [count, seen]
}
}
for ch in string {
if (ch != seen) {
put()
seen := ch
count := 0
}
count += 1
}
put()
return result
}
def unrle(coded) {
var result := ""
for [count, ch] in coded {
result += E.toString(ch) * count
}
return result
}? rle("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
# value: [[12, 'W'], [1, 'B'], [12, 'W'], [3, 'B'], [24, 'W'], [1, 'B'], [14, 'W']]
? unrle(rle("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"))
# value: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"EasyLang
func$ rlenc in$ .
for c$ in strchars in$
if c$ = c0$
cnt += 1
else
if cnt > 0
out$ &= cnt & c0$ & " "
.
c0$ = c$
cnt = 1
.
.
out$ &= cnt & c0$
return out$
.
func$ rldec in$ .
for h$ in strsplit in$ " "
c$ = substr h$ len h$ 1
for i to number h$
out$ &= c$
.
.
return out$
.
s$ = input
print s$
s$ = rlenc s$
print s$
s$ = rldec s$
print s$
#
input_data
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWWed
An important limitation: only handles repetitions of up to 9 times. Extending the algo for more is trivial, but beyond this example.
H
,p
g/\([a-zA-Z]\)\1\1\1\1\1\1\1\1/s//9\1/g
g/\([a-zA-Z]\)\1\1\1\1\1\1\1/s//8\1/g
g/\([a-zA-Z]\)\1\1\1\1\1\1/s//7\1/g
g/\([a-zA-Z]\)\1\1\1\1\1/s//6\1/g
g/\([a-zA-Z]\)\1\1\1\1/s//5\1/g
g/\([a-zA-Z]\)\1\1\1/s//4\1/g
g/\([a-zA-Z]\)\1\1/s//3\1/g
g/\([a-zA-Z]\)\1/s//2\1/g
,p
g/9\([a-zA-Z]\)/s//\1\1\1\1\1\1\1\1\1/g
g/8\([a-zA-Z]\)/s//\1\1\1\1\1\1\1\1/g
g/7\([a-zA-Z]\)/s//\1\1\1\1\1\1\1/g
g/6\([a-zA-Z]\)/s//\1\1\1\1\1\1/g
g/5\([a-zA-Z]\)/s//\1\1\1\1\1/g
g/4\([a-zA-Z]\)/s//\1\1\1\1/g
g/3\([a-zA-Z]\)/s//\1\1\1/g
g/2\([a-zA-Z]\)/s//\1\1/g
,p
Q
- Output:
$ ed -s run-length.input < run-length.ed Newline appended aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa 5a6h7mu7i6a aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa
Elena
ELENA 6.x :
import system'text;
import system'routines;
import extensions;
import extensions'text;
singleton compressor
{
string compress(string s)
{
auto tb := new TextBuilder();
int count := 0;
char current := s[0];
s.forEach::(ch)
{
if (ch == current)
{
count += 1
}
else
{
tb.writeFormatted("{0}{1}",count,current);
count := 1;
current := ch
}
};
tb.writeFormatted("{0}{1}",count,current);
^ tb
}
string decompress(string s)
{
auto tb := new TextBuilder();
char current := $0;
var a := new StringWriter();
s.forEach::(ch)
{
current := ch;
if (current.isDigit())
{
a.append(ch)
}
else
{
int count := a.toInt();
a.clear();
tb.fill(current,count)
}
};
^ tb
}
}
public program()
{
var s := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
s := compressor.compress(s);
console.printLine(s);
s := compressor.decompress(s);
console.printLine(s)
}- Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Elixir
defmodule Run_length do
def encode(str) when is_bitstring(str) do
to_char_list(str) |> encode |> to_string
end
def encode(list) when is_list(list) do
Enum.chunk_by(list, &(&1))
|> Enum.flat_map(fn chars -> to_char_list(length(chars)) ++ [hd(chars)] end)
end
def decode(str) when is_bitstring(str) do
Regex.scan(~r/(\d+)(.)/, str)
|> Enum.map_join(fn [_,n,c] -> String.duplicate(c, String.to_integer(n)) end)
end
def decode(list) when is_list(list) do
to_string(list) |> decode |> to_char_list
end
end
text = [ string: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
char_list: 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW' ]
Enum.each(text, fn {type, txt} ->
IO.puts type
txt |> IO.inspect
|> Run_length.encode |> IO.inspect
|> Run_length.decode |> IO.inspect
end)
- Output:
string "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" "12W1B12W3B24W1B14W" "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" char_list 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW' '12W1B12W3B24W1B14W' 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
Emacs Lisp
(defun run-length-encode (str)
(let (output)
(with-temp-buffer
(insert str)
(goto-char (point-min))
(while (not (eobp))
(let* ((char (char-after (point)))
(count (skip-chars-forward (string char))))
(push (format "%d%c" count char) output))))
(mapconcat #'identity (nreverse output) "")))
(require 'seq)
(defun run-length-encode (str)
(let ((grouped (mapcar #'cdr (seq-group-by #'identity (string-to-list str)))))
(apply #'concat (mapcar (lambda (items)
(format "%d%c" (length items) (car items)))
grouped))))
Erlang
A single-threaded/process version with a simple set of unit test.
-module(rle).
-export([encode/1,decode/1]).
-include_lib("eunit/include/eunit.hrl").
encode(S) ->
doEncode(string:substr(S, 2), string:substr(S, 1, 1), 1, []).
doEncode([], CurrChar, Count, R) ->
R ++ integer_to_list(Count) ++ CurrChar;
doEncode(S, CurrChar, Count, R) ->
NextChar = string:substr(S, 1, 1),
if
NextChar == CurrChar ->
doEncode(string:substr(S, 2), CurrChar, Count + 1, R);
true ->
doEncode(string:substr(S, 2), NextChar, 1,
R ++ integer_to_list(Count) ++ CurrChar)
end.
decode(S) ->
doDecode(string:substr(S, 2), string:substr(S, 1, 1), []).
doDecode([], _, R) ->
R;
doDecode(S, CurrString, R) ->
NextChar = string:substr(S, 1, 1),
IsInt = erlang:is_integer(catch(erlang:list_to_integer(NextChar))),
if
IsInt ->
doDecode(string:substr(S, 2), CurrString ++ NextChar, R);
true ->
doDecode(string:substr(S, 2), [],
R ++ string:copies(NextChar, list_to_integer(CurrString)))
end.
rle_test_() ->
PreEncoded =
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
Expected = "12W1B12W3B24W1B14W",
[
?_assert(encode(PreEncoded) =:= Expected),
?_assert(decode(Expected) =:= PreEncoded),
?_assert(decode(encode(PreEncoded)) =:= PreEncoded)
].
A version that works on character lists:
-module(rle).
-export([encode/1, decode/1]).
encode(L) -> encode(L, []).
encode([], Acc) -> {rle, lists:reverse(Acc)};
encode([H|T], []) ->
encode(T, [{1, H}]);
encode([H|T], [{Count, Char}|AT]) ->
if
H =:= Char ->
encode(T, [{Count + 1, Char}|AT]);
true ->
encode(T, [{1, H}|[{Count, Char}|AT]])
end.
decode({rle, L}) -> lists:append(lists:reverse(decode(L, []))).
decode([], Acc) -> Acc;
decode([{Count, Char}|T], Acc) ->
decode(T, [[Char || _ <- lists:seq(1, Count)]|Acc]).
Euphoria
include misc.e
function encode(sequence s)
sequence out
integer prev_char,count
if length(s) = 0 then
return {}
end if
out = {}
prev_char = s[1]
count = 1
for i = 2 to length(s) do
if s[i] != prev_char then
out &= {count,prev_char}
prev_char = s[i]
count = 1
else
count += 1
end if
end for
out &= {count,prev_char}
return out
end function
function decode(sequence s)
sequence out
out = {}
for i = 1 to length(s) by 2 do
out &= repeat(s[i+1],s[i])
end for
return out
end function
sequence s
s = encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
pretty_print(1,s,{3})
puts(1,'\n')
puts(1,decode(s))Output:
{12,'W',1,'B',12,'W',3,'B',24,'W',1,'B',14,'W'}
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
F#
open System
open System.Text.RegularExpressions
let encode data =
// encodeData : seq<'T> -> seq<int * 'T> i.e. Takes a sequence of 'T types and return a sequence of tuples containing the run length and an instance of 'T.
let rec encodeData input =
seq { if not (Seq.isEmpty input) then
let head = Seq.head input
let runLength = Seq.length (Seq.takeWhile ((=) head) input)
yield runLength, head
yield! encodeData (Seq.skip runLength input) }
encodeData data |> Seq.fold(fun acc (len, d) -> acc + len.ToString() + d.ToString()) ""
let decode str =
[ for m in Regex.Matches(str, "(\d+)(.)") -> m ]
|> List.map (fun m -> Int32.Parse(m.Groups.[1].Value), m.Groups.[2].Value)
|> List.fold (fun acc (len, s) -> acc + String.replicate len s) ""
Factor
USING: io kernel literals math.parser math.ranges sequences
sequences.extras sequences.repeating splitting.extras
splitting.monotonic strings ;
IN: rosetta-code.run-length-encoding
CONSTANT: alpha $[ CHAR: A CHAR: Z [a,b] >string ]
: encode ( str -- str )
[ = ] monotonic-split [ [ length number>string ] [ first ]
bi suffix ] map concat ;
: decode ( str -- str )
alpha split* [ odd-indices ] [ even-indices
[ string>number ] map ] bi [ repeat ] 2map concat ;
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
"12W1B12W3B24W1B14W"
[ encode ] [ decode ] bi* [ print ] bi@
- Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
FALSE
1^[^$~][$@$@=$[%%\1+\$0~]?~[@.,1\$]?%]#%\., {encode}[0[^$$'9>'0@>|~]['0-\10*+]#]n:
[n;!$~][[\$][1-\$,]#%%]#%% {decode}Fan
**
** Generates a run-length encoding for a string
**
class RLE
{
Run[] encode(Str s)
{
runs := Run[,]
s.size.times |i|
{
ch := s[i]
if (runs.size==0 || runs.last.char != ch)
runs.add(Run(ch))
runs.last.inc
}
return runs
}
Str decode(Run[] runs)
{
buf := StrBuf()
runs.each |run|
{
run.count.times { buf.add(run.char.toChar) }
}
return buf.toStr
}
Void main()
{
echo(decode(encode(
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
)))
}
}
internal class Run
{
Int char
Int count := 0
new make(Int ch) { char = ch }
Void inc() { ++count }
override Str toStr() { return "${count}${char.toChar}" }
}
Forth
variable a
: n>a (.) tuck a @ swap move a +! ;
: >a a @ c! 1 a +! ;
: encode ( c-addr +n a -- a n' )
dup a ! -rot over c@ 1 2swap 1 /string bounds ?do
over i c@ = if 1+
else n>a >a i c@ 1 then
loop n>a >a a @ over - ;
: digit? [char] 0 [ char 9 1+ literal ] within ;
: decode ( c-addr +n a -- a n' )
dup a ! 0 2swap bounds ?do
i c@ digit? if 10 * i c@ [char] 0 - + else
a @ over i c@ fill a +! 0 then
loop drop a @ over - ;
Example:
s" WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
here 1000 + encode here 2000 + decode cr 3 spaces type
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Fortran
program RLE
implicit none
integer, parameter :: bufsize = 100 ! Sets maximum size of coded and decoded strings, adjust as necessary
character(bufsize) :: teststr = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
character(bufsize) :: codedstr = "", decodedstr = ""
call Encode(teststr, codedstr)
write(*,"(a)") trim(codedstr)
call Decode(codedstr, decodedstr)
write(*,"(a)") trim(decodedstr)
contains
subroutine Encode(instr, outstr)
character(*), intent(in) :: instr
character(*), intent(out) :: outstr
character(8) :: tempstr = ""
character(26) :: validchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
integer :: a, b, c, i
if(verify(trim(instr), validchars) /= 0) then
outstr = "Invalid input"
return
end if
outstr = ""
c = 1
a = iachar(instr(1:1))
do i = 2, len(trim(instr))
b = iachar(instr(i:i))
if(a == b) then
c = c + 1
else
write(tempstr, "(i0)") c
outstr = trim(outstr) // trim(tempstr) // achar(a)
a = b
c = 1
end if
end do
write(tempstr, "(i0)") c
outstr = trim(outstr) // trim(tempstr) // achar(b)
end subroutine
subroutine Decode(instr, outstr)
character(*), intent(in) :: instr
character(*), intent(out) :: outstr
character(26) :: validchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
integer :: startn, endn, n
outstr = ""
startn = 1
do while(startn < len(trim(instr)))
endn = scan(instr(startn:), validchars) + startn - 1
read(instr(startn:endn-1), "(i8)") n
outstr = trim(outstr) // repeat(instr(endn:endn), n)
startn = endn + 1
end do
end subroutine
end program
Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
FreeBASIC
Dim As String initial, encoded, decoded
Function RLDecode(i As String) As String
Dim As Long Loop0
dim as string rCount, outP, m
For Loop0 = 1 To Len(i)
m = Mid(i, Loop0, 1)
Select Case m
Case "0" To "9"
rCount += m
Case Else
If Len(rCount) Then
outP += String(Val(rCount), m)
rCount = ""
Else
outP += m
End If
End Select
Next
RLDecode = outP
End Function
Function RLEncode(i As String) As String
Dim As String tmp1, tmp2, outP
Dim As Long Loop0, rCount
tmp1 = Mid(i, 1, 1)
tmp2 = tmp1
rCount = 1
For Loop0 = 2 To Len(i)
tmp1 = Mid(i, Loop0, 1)
If tmp1 <> tmp2 Then
outP += Ltrim(Rtrim(Str(rCount))) + tmp2
tmp2 = tmp1
rCount = 1
Else
rCount += 1
End If
Next
outP += Ltrim(Rtrim(Str(rCount)))
outP += tmp2
RLEncode = outP
End Function
Input "Type something: ", initial
encoded = RLEncode(initial)
decoded = RLDecode(encoded)
Print initial
Print encoded
Print decoded
End
- Output:
La salida es similar a la de BASIC, mostrada arriba.
FutureBasic
This gives RLE encoding for strings and RLE decoding for strings and arrays, e.g., for Conway's Game of Life
local fn encode( string as CFStringRef) as CFStringRef
CFStringRef ch, s, t
Short i, rl
s = @"" // Initalize the output string
for i = 0 to len( string ) - 1 // Encode string char by char
ch = mid( string, i, 1) // Read character at index
rl = 1 // Start run-length counter
while fn StringIsEqual( mid( string, i + rl, 1), ch )
rl ++ // Same char, so increase counter
wend
if rl == 1 then t = @"" else t = fn StringWithFormat( @"%d", rl ) // Counter as string, don't encode 1's
t = fn StringByAppendingString( t, ch ) // Add character
s = fn StringByAppendingString( s, t ) // Add to already encoded string
i += rl - 1 // Move index
next
print s
end fn
local fn decode( string as CFStringRef )
CFStringRef ch, s, t // character, outputstring, temporary string
Short i, rl // index, run length
s = @"" // Initalize the output string
for i = 0 to len( string ) - 1 // Decode input string char by char
ch = mid( string, i, 1 ) // Read character at index
if intval( ch ) == 0 // Not a digit
rl = 1
else
rl = intval( mid( string, i ) ) // Read run-length
i += fix( log10( rl ) + 1 ) // Move index past digits
ch = mid( string, i, 1 ) // Read character after run length
end if
t = fn StringByPaddingToLength( ch, rl, ch, 0 ) // Assemble temp string
s = fn StringByAppendingString( s, t ) // Add to decoded string
next
print s
end fn
local fn decode2D( string as CFStringRef ) // For Conway's Game of Life objects
Boolean a(500, 500) // Or larger to hold bigger life forms
CFStringRef ch
Short i, j, rl, f // Decoded char
Short v = 0, w = 0, x = 0, y = 0 // Temp width, max width, array coordinates
for i = 0 to len( string ) - 2 // Final char is always !
ch = mid( string, i, 1 )
if intval( ch ) == 0
rl = 1
else
rl = intval( mid( string, i ) )
i += fix( log10( rl ) + 1 )
ch = mid( string, i, 1 )
end if
select ch // Decode character as:
case @"$" : f = -1 // - new line
case @"b" : f = 0 // - dead
case @"o" : f = 1 // - live
case else : // Ignore
end select
for j = 1 to rl // Fill array with run of chars
if f = -1
x = 0 : y ++ : v = 0 // New line
else
a(x, y) = f
x ++ : v ++ : if v > w then w = v
end if
next
next
for j = 0 to y : for i = 0 to w - 1
print a(i, j);
next : print : next
end fn
fn decode( @"12W1B12W3B24W1B14W" ) // Assignment
fn encode( @"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" )
fn decode2D( @"bo$2bo$3o!" ) // Glider
handleevents // Join Mac event loopOutput:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12WB12W3B24WB14W 011 001 111
Gambas
Click this link to run this code
Public Sub Main()
Dim sString As String = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Dim siCount As Short = 1
Dim siStart As Short = 1
Dim sHold As New String[]
Dim sTemp As String
sString &= " "
Repeat
sTemp = Mid(sString, siCount, 1)
Do
Inc siCount
If Mid(sString, siCount, 1) <> sTemp Then Break
If siCount = Len(sString) Then Break
Loop
sHold.add(Str(siCount - siStart) & sTemp)
siStart = siCount
Until siCount = Len(sString)
Print sString & gb.NewLine & sHold.Join(", ")
End
Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W, 1B, 12W, 3B, 24W, 1B, 14W
Go
Decoder kind of necessary to demonstrate task requirement that I can recreate the input.
package main
import "fmt"
// encoding scheme:
// encode to byte array
// byte value < 26 means single character: byte value + 'A'
// byte value 26..255 means (byte value - 24) copies of next byte
func rllEncode(s string) (r []byte) {
if s == "" {
return
}
c := s[0]
if c < 'A' || c > 'Z' {
panic("invalid")
}
nc := byte(1)
for i := 1; i < len(s); i++ {
d := s[i]
switch {
case d != c:
case nc < (255 - 24):
nc++
continue
}
if nc > 1 {
r = append(r, nc+24)
}
r = append(r, c-'A')
if d < 'A' || d > 'Z' {
panic("invalid")
}
c = d
nc = 1
}
if nc > 1 {
r = append(r, nc+24)
}
r = append(r, c-'A')
return
}
func main() {
s := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
fmt.Println("source: ", len(s), "bytes:", s)
e := rllEncode(s)
fmt.Println("encoded:", len(e), "bytes:", e)
d := rllDecode(e)
fmt.Println("decoded:", len(d), "bytes:", d)
fmt.Println("decoded = source:", d == s)
}
func rllDecode(e []byte) string {
var c byte
var d []byte
for i := 0; i < len(e); i++ {
b := e[i]
if b < 26 {
c = 1
} else {
c = b - 24
i++
b = e[i]
}
for c > 0 {
d = append(d, b+'A')
c--
}
}
return string(d)
}
Output:
source: 67 bytes: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded: 12 bytes: [36 22 1 36 22 27 1 48 22 1 38 22] decoded: 67 bytes: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW decoded = source: true
Groovy
def rleEncode(text) {
def encoded = new StringBuilder()
(text =~ /(([A-Z])\2*)/).each { matcher ->
encoded.append(matcher[1].size()).append(matcher[2])
}
encoded.toString()
}
def rleDecode(text) {
def decoded = new StringBuilder()
(text =~ /([0-9]+)([A-Z])/).each { matcher ->
decoded.append(matcher[2] * Integer.parseInt(matcher[1]))
}
decoded.toString()
}
Test code
def text = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
def rleEncoded = rleEncode(text)
assert rleEncoded == '12W1B12W3B24W1B14W'
assert text == rleDecode(rleEncoded)
println "Original Text: $text"
println "Encoded Text: $rleEncoded"
Output:
Original Text: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded Text: 12W1B12W3B24W1B14W
Haskell
In terms of group
import Data.List (group)
-- Datatypes
type Encoded = [(Int, Char)] -- An encoded String with form [(times, char), ...]
type Decoded = String
-- Takes a decoded string and returns an encoded list of tuples
rlencode :: Decoded -> Encoded
rlencode = fmap ((,) <$> length <*> head) . group
-- Takes an encoded list of tuples and returns the associated decoded String
rldecode :: Encoded -> Decoded
rldecode = concatMap (uncurry replicate)
main :: IO ()
main = do
let input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
-- Output encoded and decoded versions of input
encoded = rlencode input
decoded = rldecode encoded
putStrLn $ "Encoded: " <> show encoded <> "\nDecoded: " <> show decoded
- Output:
Encoded: [(12,'W'),(1,'B'),(12,'W'),(3,'B'),(24,'W'),(1,'B'),(14,'W')] Decoded: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Or:
import Data.Char (isDigit)
import Data.List (group, groupBy)
runLengthEncode :: String -> String
runLengthEncode =
concatMap
( \xs@(x : _) ->
( show . length $ xs
)
<> [x]
)
. group
runLengthDecode :: String -> String
runLengthDecode =
concat . uncurry (zipWith (\[x] ns -> replicate (read ns) x))
. foldr (\z (x, y) -> (y, z : x)) ([], [])
. groupBy (\x y -> all isDigit [x, y])
main :: IO ()
main = do
let text = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
encode = runLengthEncode text
decode = runLengthDecode encode
mapM_ putStrLn [text, encode, decode]
putStrLn $ "test: text == decode => " <> show (text == decode)
- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW test: text == decode => True
In terms of span
import Data.Char (isDigit)
import Data.List (span)
encode :: String -> String
encode [] = []
encode (x : xs) =
let (run, rest) = span (x ==) xs
in x : (show . succ . length) run <> encode rest
decode :: String -> String
decode [] = []
decode (x : xs) =
let (ds, rest) = span isDigit xs
n = read ds :: Int
in replicate n x <> decode rest
main :: IO ()
main =
putStrLn encoded
>> putStrLn decoded
>> print (src == decoded)
where
src = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
encoded = encode src
decoded = decode encoded
- Output:
W12B1W12B3W24B1W14 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW True
As a fold
----------------------- RUN LENGTHS ----------------------
runLengths :: String -> [(Int, Char)]
runLengths "" = []
runLengths s = uncurry (:) (foldr go ((0, ' '), []) s)
where
go c ((0, _), xs) = ((1, c), xs)
go c ((n, x), xs)
| c == x = ((succ n, x), xs)
| otherwise = ((1, c), (n, x) : xs)
--------------------------- TEST -------------------------
main :: IO ()
main = do
let testString =
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWW"
<> "WWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
encoded = runLengths testString
putStrLn $ showLengths encoded
print $
concatMap (uncurry replicate) encoded == testString
------------------------- DISPLAY ------------------------
showLengths :: [(Int, Char)] -> String
showLengths [] = []
showLengths ((n, c) : xs) = show n <> [c] <> showLengths xs
- Output:
12W1B12W3B24W1B14W True
Icon and Unicon
Sample output:
s="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" s1="12W1B12W3B24W1B14W" s2="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" Encode/Decode worked.
J
Solution:
rle=: ;@(<@(":@(#-.1:),{.);.1~ 1, 2 ~:/\ ])
rld=: ;@(-.@e.&'0123456789' <@({:#~1{.@,~".@}:);.2 ])
Example:
rle 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
12W1B12W3B24W1B14W
rld '12W1B12W3B24W1B14W'
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Note that this implementation fails for the empty case. Here's a version that fixes that:
rle=: ;@(<@(":@#,{.);.1~ 2 ~:/\ (a.{.@-.{.),])
Other approaches include using rle ::(''"_) or rle^:(*@#) or equivalent variations on the original sentence.
Alternative Implementation
A numeric approach, based on a discussion in the J forums (primarily Pascal Jasmin and Marshall Lochbaum):
torle=: (#, {.);.1~ 1,2 ~:/\ ]
frle=: #/@|:
Task example:
torle a.i.'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
12 87
1 66
12 87
3 66
24 87
1 66
14 87
u: frle torle a.i.'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Note that this approach also fails on the empty case.
Java
This can be achieved using regular expression capturing
import java.util.regex.Matcher;
import java.util.regex.Pattern;
String encode(String string) {
Pattern pattern = Pattern.compile("(.)\\1*");
Matcher matcher = pattern.matcher(string);
StringBuilder encoded = new StringBuilder();
while (matcher.find()) {
encoded.append(matcher.group().length());
encoded.append(matcher.group().charAt(0));
}
return encoded.toString();
}
String decode(String string) {
Pattern pattern = Pattern.compile("(\\d+)(.)");
Matcher matcher = pattern.matcher(string);
StringBuilder decoded = new StringBuilder();
int count;
while (matcher.find()) {
count = Integer.parseInt(matcher.group(1));
decoded.append(matcher.group(2).repeat(count));
}
return decoded.toString();
}
string = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded = 12W1B12W3B24W1B14W decoded = WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW string.equals(decoded) = true string = https://www.rosettacode.org/ encoded = 1h2t1p1s1:2/3w1.1r1o1s1e2t1a1c1o1d1e1.1o1r1g1/ decoded = https://www.rosettacode.org/ string.equals(decoded) = true
An alternate demonstration
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RunLengthEncoding {
public static String encode(String source) {
StringBuffer dest = new StringBuffer();
for (int i = 0; i < source.length(); i++) {
int runLength = 1;
while (i+1 < source.length() && source.charAt(i) == source.charAt(i+1)) {
runLength++;
i++;
}
dest.append(runLength);
dest.append(source.charAt(i));
}
return dest.toString();
}
public static String decode(String source) {
StringBuffer dest = new StringBuffer();
Pattern pattern = Pattern.compile("[0-9]+|[a-zA-Z]");
Matcher matcher = pattern.matcher(source);
while (matcher.find()) {
int number = Integer.parseInt(matcher.group());
matcher.find();
while (number-- != 0) {
dest.append(matcher.group());
}
}
return dest.toString();
}
public static void main(String[] args) {
String example = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
System.out.println(encode(example));
System.out.println(decode("1W1B1W1B1W1B1W1B1W1B1W1B1W1B"));
}
}
Tests:
import static org.junit.Assert.assertEquals;
import org.junit.Test;
public class RunLengthEncodingTest {
private RLE = new RunLengthEncoding();
@Test
public void encodingTest() {
assertEquals("1W", RLE.encode("W"));
assertEquals("4W", RLE.encode("WWWW"));
assertEquals("5w4i7k3i6p5e4d2i1a",
RLE.encode("wwwwwiiiikkkkkkkiiippppppeeeeeddddiia"));
assertEquals("12B1N12B3N24B1N14B",
RLE.encode("BBBBBBBBBBBBNBBBBBBBBBBBBNNNBBBBBBBBBBBBBBBBBBBBBBBBNBBBBBBBBBBBBBB"));
assertEquals("12W1B12W3B24W1B14W",
RLE.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"));
assertEquals("1W1B1W1B1W1B1W1B1W1B1W1B1W1B", RLE.encode("WBWBWBWBWBWBWB"));
}
@Test
public void decodingTest() {
assertEquals("W", RLE.decode("1W"));
assertEquals("WWWW", RLE.decode("4W"));
assertEquals("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
RLE.decode("12W1B12W3B24W1B14W"));
assertEquals("WBWBWBWBWBWBWB", RLE.decode("1W1B1W1B1W1B1W1B1W1B1W1B1W1B"));
assertEquals("WBWBWBWBWBWBWB", RLE.decode("1W1B1W1B1W1B1W1B1W1B1W1B1W1B"));
}
}
JavaScript
ES5
Here's an encoding method that walks the input string character by character
function encode(input) {
var encoding = [];
var prev, count, i;
for (count = 1, prev = input[0], i = 1; i < input.length; i++) {
if (input[i] != prev) {
encoding.push([count, prev]);
count = 1;
prev = input[i];
}
else
count ++;
}
encoding.push([count, prev]);
return encoding;
}
Here's an encoding method that uses a regular expression to grab the character runs (
for the forEach method)
function encode_re(input) {
var encoding = [];
input.match(/(.)\1*/g).forEach(function(substr){ encoding.push([substr.length, substr[0]]) });
return encoding;
}
And to decode (see Repeating a string)
function decode(encoded) {
var output = "";
encoded.forEach(function(pair){ output += new Array(1+pair[0]).join(pair[1]) })
return output;
}
ES6
By defining a generic group function:
(() => {
'use strict';
// runLengthEncode :: String -> [(Int, Char)]
const runLengthEncoded = s =>
group(s.split('')).map(
cs => [cs.length, cs[0]]
);
// runLengthDecoded :: [(Int, Char)] -> String
const runLengthDecoded = pairs =>
pairs.map(([n, c]) => c.repeat(n)).join('');
// ------------------------TEST------------------------
const main = () => {
const
xs = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWW' +
'WWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW',
ys = runLengthEncoded(xs);
console.log('From: ', show(xs));
[ys, runLengthDecoded(ys)].forEach(
x => console.log(' -> ', show(x))
)
};
// ----------------------GENERIC-----------------------
// group :: [a] -> [[a]]
const group = xs => {
// A list of lists, each containing only equal elements,
// such that the concatenation of these lists is xs.
const go = xs =>
0 < xs.length ? (() => {
const
h = xs[0],
i = xs.findIndex(x => h !== x);
return i !== -1 ? (
[xs.slice(0, i)].concat(go(xs.slice(i)))
) : [xs];
})() : [];
return go(xs);
};
// show :: a -> String
const show = JSON.stringify;
// MAIN ---
return main();
})();
- Output:
From: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" -> [[12,"W"],[1,"B"],[12,"W"],[3,"B"],[24,"W"],[1,"B"],[14,"W"]] -> "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
A .reduce() based one-liner
const rlEncode = (s: string) => s.match(/(.)\1*/g).reduce((result,char) => result+char.length+char[0],"")
const rlValidate = (s: string) => /^(\d+\D)+$/.test(s)
const rlDecode = (s: string) => rlValidate(s) ? s.match(/(\d[a-z\s])\1*/ig).reduce((res,p) => res+p[p.length-1].repeat(parseInt(p)),"") : Error("Invalid rl")
jq
Note: "run_length_decode" as defined below requires a version of jq with regex support.
Utility function:
def runs:
reduce .[] as $item
( [];
if . == [] then [ [ $item, 1] ]
else .[length-1] as $last
| if $last[0] == $item then .[length-1] = [$item, $last[1] + 1]
else . + [[$item, 1]]
end
end ) ;Run-length encoding and decoding:
def run_length_encode:
explode | runs | reduce .[] as $x (""; . + "\($x[1])\([$x[0]]|implode)");
def run_length_decode:
reduce (scan( "[0-9]+[A-Z]" )) as $pair
( "";
($pair[0:-1] | tonumber) as $n
| $pair[-1:] as $letter
| . + ($n * $letter)) ;Example:
"ABBCCC" | run_length_encode | run_length_decode- Output:
$ jq -n -f Run_length_encoding.jq
"ABBCCC"
Julia
using IterTools
encode(str::String) = collect((length(g), first(g)) for g in groupby(first, str))
decode(cod::Vector) = join(repeat("$l", n) for (n, l) in cod)
for original in ["aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa", "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"]
encoded = encode(original)
decoded = decode(encoded)
println("Original: $original\n -> encoded: $encoded\n -> decoded: $decoded")
end
- Output:
Original: aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa
-> encoded: Tuple{Int64,Char}[(5, 'a'), (6, 'h'), (7, 'm'), (1, 'u'), (7, 'i'), (6, 'a')]
-> decoded: aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa
Original: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
-> encoded: Tuple{Int64,Char}[(12, 'W'), (1, 'B'), (12, 'W'), (3, 'B'), (24, 'W'), (1, 'B'), (14, 'W')]
-> decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
K
rle: {,/($-':i,#x),'x@i:&1,~=':x}
rld: {d:"0123456789"; ,/(.(d," ")@d?/:x)#'x _dvl d}
Example:
rle "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
"12W1B12W3B24W1B14W"
rld "12W1B12W3B24W1B14W"
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Kotlin
Tail recursive implementation of Run Length Encoding
tailrec fun runLengthEncoding(text:String,prev:String=""):String {
if (text.isEmpty()){
return prev
}
val initialChar = text.get(0)
val count = text.takeWhile{ it==initialChar }.count()
return runLengthEncoding(text.substring(count),prev + "$count$initialChar" )
}
fun main(args: Array<String>) {
assert(runLengthEncoding("TTESSST") == "2T1E3S1T")
assert(runLengthEncoding("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
== "12W1B12W3B24W1B14W")
}
Lasso
define rle(str::string)::string => {
local(orig = #str->values->asCopy,newi=array, newc=array, compiled=string)
while(#orig->size) => {
if(not #newi->size) => {
#newi->insert(1)
#newc->insert(#orig->first)
#orig->remove(1)
else
if(#orig->first == #newc->last) => {
#newi->get(#newi->size) += 1
else
#newi->insert(1)
#newc->insert(#orig->first)
}
#orig->remove(1)
}
}
loop(#newi->size) => {
#compiled->append(#newi->get(loop_count)+#newc->get(loop_count))
}
return #compiled
}
define rlde(str::string)::string => {
local(o = string)
while(#str->size) => {
loop(#str->size) => {
if(#str->isualphabetic(loop_count)) => {
if(loop_count == 1) => {
#o->append(#str->get(loop_count))
#str->removeLeading(#str->get(loop_count))
loop_abort
}
local(num = integer(#str->substring(1,loop_count)))
#o->append(#str->get(loop_count)*#num)
#str->removeLeading(#num+#str->get(loop_count))
loop_abort
}
}
}
return #o
}
//Tests:
rle('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW')
rle('dsfkjhhkdsjfhdskhshdjjfhhdlsllw')
rlde('12W1B12W3B24W1B14W')
rlde('1d1s1f1k1j2h1k1d1s1j1f1h1d1s1k1h1s1h1d2j1f2h1d1l1s2l1w')
- Output:
12W1B12W3B24W1B14W 1d1s1f1k1j2h1k1d1s1j1f1h1d1s1k1h1s1h1d2j1f2h1d1l1s2l1w WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW dsfkjhhkdsjfhdskhshdjjfhhdlsllw
Liberty BASIC
mainwin 100 20
'In$ ="aaaaaaaaaaaaaaaaaccbbbbbbbbbbbbbbba" ' testing...
In$ ="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
' Out$= "12W1B12W3B24W1B14W"
Out$ =Encoded$( In$)
Inv$ =Decoded$( Out$)
print " Supplied string ="; In$
Print " RLE version ="; Out$
print " Decoded back to ="; Inv$
end
function Encoded$( k$)
r$ =""
r =1
for i =2 to len( k$)
prev$ =mid$( k$, i -1, 1)
c$ =mid$( k$, i, 1)
if c$ =prev$ then ' entering a run of this character
r =r +1
else ' it occurred only once
r$ =r$ +str$( r) +prev$
r =1
end if
next i
r$ =r$ +str$( r) +c$
Encoded$ =r$
end function
function Decoded$( k$)
r$ =""
v =0
for i =1 to len( k$)
i$ =mid$( k$, i, 1)
if instr( "0123456789", i$) then
v =v *10 +val( i$)
else
for m =1 to v
r$ =r$ +i$
next m
v =0
end if
next i
Decoded$ =r$
end functionLiveCode
function rlEncode str
local charCount
put 1 into charCount
repeat with i = 1 to the length of str
if char i of str = char (i + 1) of str then
add 1 to charCount
else
put char i of str & charCount after rle
put 1 into charCount
end if
end repeat
return rle
end rlEncode
function rlDecode str
repeat with i = 1 to the length of str
if char i of str is not a number then
put char i of str into curChar
put 0 into curNum
else
repeat with n = i to len(str)
if isnumber(char n of str) then
put char n of str after curNum
else
put repeatString(curChar,curNum) after rldec
put n - 1 into i
exit repeat
end if
end repeat
end if
if i = len(str) then --dump last char
put repeatString(curChar,curNum) after rldec
end if
end repeat
return rldec
end rlDecode
function repeatString str,rep
repeat rep times
put str after repStr
end repeat
return repStr
end repeatStringLogo
to encode :str [:out "||] [:count 0] [:last first :str]
if empty? :str [output (word :out :count :last)]
if equal? first :str :last [output (encode bf :str :out :count+1 :last)]
output (encode bf :str (word :out :count :last) 1 first :str)
end
to reps :n :w
output ifelse :n = 0 ["||] [word :w reps :n-1 :w]
end
to decode :str [:out "||] [:count 0]
if empty? :str [output :out]
if number? first :str [output (decode bf :str :out 10*:count + first :str)]
output (decode bf :str word :out reps :count first :str)
end
make "foo "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
make "rle encode :foo
show equal? :foo decode :rleLua
local C, Ct, R, Cf, Cc = lpeg.C, lpeg.Ct, lpeg.R, lpeg.Cf, lpeg.Cc
astable = Ct(C(1)^0)
function compress(t)
local ret = {}
for i, v in ipairs(t) do
if t[i-1] and v == t[i-1] then
ret[#ret - 1] = ret[#ret - 1] + 1
else
ret[#ret + 1] = 1
ret[#ret + 1] = v
end
end
t = ret
return table.concat(ret)
end
q = io.read()
print(compress(astable:match(q)))
undo = Ct((Cf(Cc"0" * C(R"09")^1, function(a, b) return 10 * a + b end) * C(R"AZ"))^0)
function decompress(s)
t = undo:match(s)
local ret = ""
for i = 1, #t - 1, 2 do
for _ = 1, t[i] do
ret = ret .. t[i+1]
end
end
return ret
end
M2000 Interpreter
Module RLE_example {
inp$="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Print "Input: ";inp$
Function RLE$(r$){
Function rle_run$(&r$) {
if len(r$)=0 then exit
p=1
c$=left$(r$,1)
while c$=mid$(r$, p, 1) {p++}
=format$("{0}{1}",p-1, c$)
r$=mid$(r$, p)
}
def repl$
while len(r$)>0 {repl$+=rle_run$(&r$)}
=repl$
}
RLE_encode$=RLE$(inp$)
Print "RLE Encoded: ";RLE_encode$
Function RLE_decode$(r$) {
def repl$
def long m, many=1
while r$<>"" and many>0 {
many=val(r$, "INT", &m)
repl$+=string$(mid$(r$, m, 1), many)
r$=mid$(r$,m+1)
}
=repl$
}
RLE_decode$=RLE_decode$(RLE_encode$)
Print "RLE Decoded: ";RLE_decode$
Print "Checked: ";RLE_decode$=inp$
}
RLE_example- Output:
Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW RLE Encoded: 12W1B12W3B24W1B14W RLE Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Checked: True
Mathematica /Wolfram Language
The function
RunLengthEncode[input_String]:= (l |-> {First@l, Length@l}) /@ (Split@Characters@input)
takes as input an arbitrary string of characters and returns a list of {c, n} pairs, where c is the character and n is the number of repeats. The function
RunLengthDecode[input_List]:= ConstantArray @@@ input // Flatten // StringJoin
recreates the string.
Example: For the string
mystring="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
here is the run-length encoding:
rle = RunLengthEncode[mystring]
{{"W", 12}, {"B", 1}, {"W", 12}, {"B", 3}, {"W", 24}, {"B", 1}, {"W", 14}}
Check that the input string is recreated:
mystring == RunLengthDecode[rle]
True
Maxima
To encode
rle(a) := block(
[n: slength(a), b: "", c: charat(a, 1), k: 1],
for i from 2 thru n do
if cequal(c, charat(a, i)) then k: k + 1 else (b: sconcat(b, k, c), c: charat(a, i), k: 1),
sconcat(b, k, c)
)$
To decode
/* Function to return a list where all but the last entries are integers */
intbucket(lst):=block(bucket:[],while integerp(first(lst)) do (push(first(lst),bucket),lst:rest(lst)),lst:append(reverse(bucket),[first(lst)]));
/* Run-length decoding */
rld(string_list):=block(
coref:map(eval_string,charlist(string_list)),
listcharact:sublist(coref,lambda([x],integerp(x)=false)),
map(intbucket,append([coref],makelist(coref:rest(coref,length(intbucket(coref))),length(listcharact)-1))),
makelist(sublist(%%[i],integerp),i,1,length(%%)),
map(eval_string,makelist(apply(concat,%%[i]),i,1,length(%%))),
makelist(smake(%%[i],string(listcharact[i])),i,1,length(listcharact)),
apply(concat,%%));
Output
rle("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW");
"12W1B12W3B24W1B14W"
rld(%);
/* "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" */
MMIX
LOC Data_Segment
GREG @
Buf OCTA 0,0,0,0 integer print buffer
Char BYTE 0,0 single char print buffer
task BYTE "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWW"
BYTE "WWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",0
len GREG @-1-task
// task should become this
tEnc BYTE "12W1B12W3B24W1B14W",0
GREG @
// tuple array for encoding purposes
// each tuple is a tetra (4 bytes long or 2 wydes long)
// (c,l) in which c is a char and l = number of chars c
// high wyde of the tetra contains the char
// low wyde .. .. .. contains the length
RLE TETRA 0
LOC #100 locate program
GREG @
// print number to stdout
// destroys input arg $3 !
Prt64 LDA $255,Buf+23 points to LSD
// do
2H DIV $3,$3,10 (N,R) = divmod (N,10)
GET $13,rR get remainder
INCL $13,'0' convert to ascii
STBU $13,$255 store ascii digit
BZ $3,3F
SUB $255,$255,1 move pointer down
JMP 2B While N !=0
3H TRAP 0,Fputs,StdOut print number to standard out
GO $127,$127,0 return
GREG @
// print char to stdout
PChar LDA $255,Char
STBU $4,$255
TRAP 0,Fputs,StdOut
GO $127,$127,0
GREG @
// encode routine
// $0 string pointer
// $1 index var
// $2 pointer to tuple array
// $11 temp var tuple
Encode SET $1,0 initialize index = 0
SET $11,0 postion in string = 0
LDBU $3,$0,$1 get first char
ADDU $6,$3,0 remember it
do
1H INCL $1,1 repeat incr index
LDBU $3,$0,$1 get a char
BZ $3,2F if EOS then finish
CMP $7,$3,$6
PBZ $7,1B while new == old
XOR $4,$4,$4 new tuple
ADDU $4,$6,0
SLU $4,$4,16 old char to tuple -> (c,_)
SUB $7,$1,$11 length = index - previous position
ADDU $11,$1,0 incr position
OR $4,$4,$7 length l to tuple -> (c,l)
STT $4,$2 put tuple in array
ADDU $6,$3,0 remember new char
INCL $2,4 incr 'tetra' pointer
JMP 1B loop
2H XOR $4,$4,$4 put last tuple in array
ADDU $4,$6,0
SLU $4,$4,16
SUB $7,$1,$11
ADDU $11,$1,0
OR $4,$4,$7
STT $4,$2
GO $127,$127,0 return
GREG @
Main LDA $0,task pointer uncompressed string
LDA $2,RLE pointer tuple array
GO $127,Encode encode string
LDA $2,RLE points to start tuples
SET $5,#ffff mask for extracting length
1H LDTU $3,$2 while not End of Array
BZ $3,2F
SRU $4,$3,16 char = (c,_)
AND $3,$3,$5 length = (_,l)
GO $127,Prt64 print length
GO $127,PChar print char
INCL $2,4 incr tuple pointer
JMP 1B wend
2H SET $4,#a print NL
GO $127,PChar
// decode using the RLE tuples
LDA $2,RLE pointer tuple array
SET $5,#ffff mask
1H LDTU $3,$2 while not End of Array
BZ $3,2F
SRU $4,$3,16 char = (c,_)
AND $3,$3,$5 length = (_,l)
// for (i=0;i<length;i++) {
3H GO $127,PChar print a char
SUB $3,$3,1
PBNZ $3,3B
INCL $2,4
JMP 1B }
2H SET $4,#a print NL
GO $127,PChar
TRAP 0,Halt,0 EXIT
Example run encode --> decode:
~/MIX/MMIX/Rosetta> mmix rle 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
newLISP
Let's first create a useful general purpose function.
;; Since newLISP has dynamic scope, use a namespace or context
;; to avoid variable capture.
(context 'monotonic-slices)
(define (monotonic-slices:monotonic-slices lst (key-func or) (cmp =))
(let (result '() tmp '() old-key 0 new-key 0)
(dolist (x lst)
(set 'new-key (key-func x))
(cond ((empty? tmp) (push x tmp))
((cmp new-key old-key) (push x tmp))
(true (push (reverse tmp) result) (set 'tmp (list x))))
(set 'old-key new-key))
(unless (empty? tmp) (push (reverse tmp) result))
(reverse result)))
(context MAIN)
(monotonic-slices '(0 0 2 3 3 3 4 5 5 5 5) )
((0 0) (2) (3 3 3) (4) (5 5 5 5))
(define (compress str)
(apply string (flat
(map
(fn (xs) (list (length xs) (first xs)))
(monotonic-slices (explode str))))))
(compress
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
"12W1B12W3B24W1B14W"
(define (decompress str)
(apply ;; Use for fold or reduce.
(fn (built a b) (push (dup (b 0) (int (join a))) built -1))
(cons ""
(monotonic-slices
(explode str)
(fn (c) (<= "0" c "9"))))
3))
(decompress "12W1B12W3B24W1B14W")
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Nim
import parseutils, strutils
proc compress(input: string): string =
var
count = 1
prev = '\0'
for ch in input:
if ch != prev:
if prev != '\0':
result.add $count & prev
count = 1
prev = ch
else:
inc count
result.add $count & prev
proc uncompress(text: string): string =
var start = 0
var count: int
while true:
let n = text.parseInt(count, start)
if n == 0 or start + n >= text.len:
raise newException(ValueError, "corrupted data.")
inc start, n
result.add repeat(text[start], count)
inc start
if start == text.len: break
const Text = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
echo "Text: ", Text
let compressed = Text.compress()
echo "Compressed: ", compressed
echo "Uncompressed: ", compressed.uncompress()
- Output:
Text: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Compressed: 12W1B12W3B24W1B14W Uncompressed: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Objeck
use RegEx;
class RunLengthEncoding {
function : Main(args : String[]) ~ Nil {
input := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
encoded := Encode(input);
"encoding: {$encoded}"->PrintLine();
test := encoded->Equals("12W1B12W3B24W1B14W");
"encoding match: {$test}"->PrintLine();
decoded := Decode(encoded);
test := input->Equals(decoded);
"decoding match: {$test}"->PrintLine();
}
function : Encode(source : String) ~ String {
dest := "";
each(i : source) {
runLength := 1;
while(i+1 < source->Size() & source->Get(i) = source->Get(i+1)) {
runLength+= 1;
i+= 1;
};
dest->Append(runLength);
dest->Append(source->Get(i));
};
return dest;
}
function : Decode(source : String) ~ String {
output := "";
regex := RegEx->New("[0-9]+|([A-Z]|[a-z])");
found := regex->Find(source);
count : Int;
each(i : found) {
if(i % 2 = 0) {
count := found->Get(i)->As(String)->ToInt();
}
else {
letter := found->Get(i)->As(String);
while(count <> 0) {
output->Append(letter);
count -= 1;
};
};
};
return output;
}
}encoding: 12W1B12W3B24W1B14W encoding match: true decoding match: true
Objective-C
See Run-length encoding/Objective-C
OCaml
let encode str =
let len = String.length str in
let rec aux i acc =
if i >= len then List.rev acc
else
let c1 = str.[i] in
let rec aux2 j =
if j >= len then (c1, j-i)
else
let c2 = str.[j] in
if c1 = c2
then aux2 (j+1)
else (c1, j-i)
in
let (c,n) as t = aux2 (i+1) in
aux (i+n) (t::acc)
in
aux 0 []
;;
let decode lst =
let l = List.map (fun (c,n) -> String.make n c) lst in
(String.concat "" l)
let () =
let e = encode "aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa" in
List.iter (fun (c,n) ->
Printf.printf " (%c, %d);\n" c n;
) e;
print_endline (decode [('a', 5); ('h', 6); ('m', 7); ('u', 1); ('i', 7); ('a', 6)]);
;;
- Using regular expressions
#load "str.cma";;
open Str
let encode =
global_substitute (Str.regexp "\\(.\\)\\1*")
(fun s -> string_of_int (String.length (matched_string s)) ^
matched_group 1 s)
let decode =
global_substitute (Str.regexp "\\([0-9]+\\)\\([^0-9]\\)")
(fun s -> String.make (int_of_string (matched_group 1 s))
(matched_group 2 s).[0])
let () =
print_endline (encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW");
print_endline (decode "12W1B12W3B24W1B14W");
Oforth
: encode(s)
StringBuffer new
s group apply(#[ tuck size asString << swap first <<c ]) ;
: decode(s)
| c i |
StringBuffer new
0 s forEach: c [
c isDigit ifTrue: [ 10 * c asDigit + continue ]
loop: i [ c <<c ] 0
]
drop ;- Output:
>"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" encode .s [1] (StringBuffer) 12W1B12W3B24W1B14W ok >decode .s [1] (StringBuffer) WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW ok
Ol
(define (RLE str)
(define iter (string->list str))
(let loop ((iter iter) (chr (car iter)) (n 0) (rle '()))
(cond
((null? iter)
(reverse (cons (cons n chr) rle)))
((char=? chr (car iter))
(loop (cdr iter) chr (+ n 1) rle))
(else
(loop (cdr iter) (car iter) 1 (cons (cons n chr) rle))))))
(define (decode rle)
(apply string-append (map (lambda (p)
(make-string (car p) (cdr p))) rle)))
Test:
(define str "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
(print str)
(define rle (RLE str))
(for-each (lambda (pair)
(print (car pair) " : " (string (cdr pair))))
rle)
(print (decode rle))
- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12 : W 1 : B 12 : W 3 : B 24 : W 1 : B 14 : W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Oz
declare
fun {RLEncode Xs}
for G in {Group Xs} collect:C do
{C {Length G}#G.1}
end
end
fun {RLDecode Xs}
for C#Y in Xs append:Ap do
{Ap {Replicate Y C}}
end
end
%% Helpers
%% e.g. "1122" -> ["11" "22"]
fun {Group Xs}
case Xs of nil then nil
[] X|Xr then
Ys Zs
{List.takeDropWhile Xr fun {$ W} W==X end ?Ys ?Zs}
in
(X|Ys) | {Group Zs}
end
end
%% e.g. 3,4 -> [3 3 3 3]
fun {Replicate X N}
case N of 0 then nil
else X|{Replicate X N-1}
end
end
Data = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Enc = {RLEncode Data}
in
{System.showInfo Data}
{Show Enc}
{System.showInfo {RLDecode Enc}}PARI/GP
rle(s)={
if(s=="", return(s));
my(v=Vec(s),cur=v[1],ct=1,out="");
v=concat(v,99); \\ sentinel
for(i=2,#v,
if(v[i]==cur,
ct++
,
out=Str(out,ct,cur);
cur=v[i];
ct=1
)
);
out
};
elr(s)={
if(s=="", return(s));
my(v=Vec(s),ct=eval(v[1]),out="");
v=concat(v,99); \\ sentinel
for(i=2,#v,
if(v[i]>="0" && v[i]<="9",
ct=10*ct+eval(v[i])
,
for(j=1,ct,out=Str(out,v[i]));
ct=0
)
);
out
};
rle("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
elr(%)Output:
%1 = "12W1B12W3B24W1B14W" %2 = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Pascal
Program RunLengthEncoding(output);
procedure encode(s: string; var counts: array of integer; var letters: string);
var
i, j: integer;
begin
j := 0;
letters := '';
if length(s) > 0 then
begin
j := 1;
letters := letters + s[1];
counts[1] := 1;
for i := 2 to length(s) do
if s[i] = letters[j] then
inc(counts[j])
else
begin
inc(j);
letters := letters + s[i];
counts[j] := 1;
end;
end;
end;
procedure decode(var s: string; counts: array of integer; letters: string);
var
i, j: integer;
begin
s := '';
for i := 1 to length(letters) do
for j := 1 to counts[i] do
s := s + letters[i];
end;
var
s: string;
counts: array of integer;
letters: string;
i: integer;
begin
s := 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWW';
writeln(s);
setlength(counts, length(s));
encode(s, counts, letters);
for i := 1 to length(letters) - 1 do
write(counts[i], ' * ', letters[i], ', ');
writeln(counts[length(letters)], ' * ', letters[length(letters)]);
decode(s, counts, letters);
writeln(s);
end.
Output:
:> ./RunLengthEncoding WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWW 12 * W, 1 * B, 12 * W, 3 * B, 24 * W, 1 * B, 13 * W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWW
Perl
Simple version using ASCII numerals as length markers, like the example in the task description (won't work correctly on input strings that already contain digits):
sub encode {
shift =~ s/(.)\1*/length($&).$1/grse;
}
sub decode {
shift =~ s/(\d+)(.)/$2 x $1/grse;
}
Modified version that can take arbitrary byte strings as input (produces encoded byte strings that are compatible with the C solution):
sub encode {
shift =~ s/(.)\1{0,254}/pack("C", length($&)).$1/grse;
}
sub decode {
shift =~ s/(.)(.)/$2 x unpack("C", $1)/grse;
}
Further modified version that supports compact representation of longer non-repeating substrings, just like the C solution (so should be fully compatible with that solution for both encoding and decoding):
sub encode {
my $str = shift;
my $ret = "";
my $nonrep = "";
while ($str =~ m/(.)\1{0,127}|\z/gs) {
my $len = length($&);
if (length($nonrep) && (length($nonrep) == 127 || $len != 1)) {
$ret .= pack("C", 128 + length($nonrep)) . $nonrep;
$nonrep = "";
}
if ($len == 1) { $nonrep .= $1 }
elsif ($len > 1) { $ret .= pack("C", $len) . $1 }
}
return $ret;
}
sub decode {
my $str = shift;
my $ret = "";
for (my $i = 0; $i < length($str);) {
my $len = unpack("C", substr($str, $i, 1));
if ($len <= 128) {
$ret .= substr($str, $i + 1, 1) x $len;
$i += 2;
}
else {
$ret .= substr($str, $i + 1, $len - 128);
$i += 1 + $len - 128;
}
}
return $ret;
}Demonstration of the third version:
use Data::Dump qw(dd);
dd my $str = "XXXXXABCDEFGHIoooooooooooooooooooooooooAAAAAA";
dd my $enc = encode($str);
dd decode($enc);- Output:
"XXXXXABCDEFGHIoooooooooooooooooooooooooAAAAAA" "\5X\x89ABCDEFGHI\31o\6A" "XXXXXABCDEFGHIoooooooooooooooooooooooooAAAAAA"
Phix
Based on Euphoria, but uses a few string in place of sequence.
with javascript_semantics function encode(string s) sequence r = {} if length(s) then integer ch = s[1], count = 1 for i=2 to length(s) do if s[i]!=ch then r &= {count,ch} ch = s[i] count = 1 else count += 1 end if end for r &= {count,ch} end if return r end function function decode(sequence s) string r = "" for i=1 to length(s) by 2 do r &= repeat(s[i+1],s[i]) end for return r end function sequence s = encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW") ?s ?decode(s)
- Output:
Note the character hints are desktop/Phix only and don't appear under p2js.
{12,87'W',1,66'B',12,87'W',3,66'B',24,87'W',1,66'B',14,87'W'}
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
PHP
<?php
function encode($str)
{
return preg_replace_callback('/(.)\1*/', function ($match) {
return strlen($match[0]) . $match[1];
}, $str);
}
function decode($str)
{
return preg_replace_callback('/(\d+)(\D)/', function($match) {
return str_repeat($match[2], $match[1]);
}, $str);
}
echo encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'), PHP_EOL;
echo decode('12W1B12W3B24W1B14W'), PHP_EOL;
?>Picat
While loop
Quite slow.
rle(S) = RLE =>
RLE = "",
Char = S[1],
I = 2,
Count = 1,
while (I <= S.len)
if Char == S[I] then
Count := Count + 1
else
RLE := RLE ++ Count.to_string() ++ Char.to_string(),
Count := 1,
Char := S[I]
end,
I := I + 1
end,
RLE := RLE ++ Count.to_string() ++ Char.to_string().Using positions of different chars
Much faster than rle/1.
rle2(S) = RLE =>
Ix = [1] ++ [I : I in 2..S.len, S[I] != S[I-1]] ++ [S.len+1],
Diffs = diff(Ix),
RLE = [Diffs[I].to_string() ++ S[Ix[I]].to_string() : I in 1..Diffs.len].join('').Recursive approach
The fastest version.
rle3(S) = RLE =>
rle3(S.tail(),S[1],1,[],RLE).
rle3([],LastChar,Count,RLE1,RLE) =>
RLE = (RLE1 ++ [Count.to_string(),LastChar.to_string()]).join('').
rle3([C|T],LastChar,Count,RLE1,RLE) =>
C == LastChar ->
rle3(T,C,Count+1,RLE1,RLE)
;
rle3(T,C,1,RLE1++[Count.to_string()++LastChar.to_string()],RLE).Test
Encode and decode (only using rle3/1):
go =>
S = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWWA",
println(S),
RLE = rle3(S),
println(rle=RLE),
D = rl_decode(RLE),
println(D),
if D == S then
println(ok)
else
println(not_ok)
end,
nl.- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWWA rle = 12W1B12W3B24W1B14W1A WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWWA ok
Benchmark on larger string
A benchmark on a larger string (30_000) clearly shows that rle3/1 is the fastest.
go2 =>
_ = random2(),
Alpha = "AB",
Len2 = Alpha.len,
_ = random2(),
S = [Alpha[random(1,Len2)] : _ in 1..30_000],
if S.len < 200 then println(s=S) end ,
println("rle/1:"),
time(_=rle(S)),
println("rle2/1:"),
time(_=rle2(S)),
println("rle3/1:"),
time(_=rle3(S)),
nl.- Output:
rle/1: CPU time 4.02 seconds. rle3/1: CPU time 2.422 seconds. rle3/1: CPU time 0.812 seconds.
PicoLisp
(de encode (Str)
(pack
(make
(for (Lst (chop Str) Lst)
(let (N 1 C)
(while (= (setq C (pop 'Lst)) (car Lst))
(inc 'N) )
(link N C) ) ) ) ) )
(de decode (Str)
(pack
(make
(let N 0
(for C (chop Str)
(if (>= "9" C "0")
(setq N (+ (format C) (* 10 N)))
(do N (link C))
(zero N) ) ) ) ) ) )
(and
(prinl "Data: " "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
(prinl "Encoded: " (encode @))
(prinl "Decoded: " (decode @)) )Output:
Data: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded: 12W1B12W3B24W1B14W Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
PL/I
declare (c1, c2) character (1);
declare run_length fixed binary;
declare input file;
open file (input) title ('/RLE.DAT,type(text),recsize(20000)');
on endfile (input) go to epilog;
get file (input) edit (c1) (a(1));
run_length = 1;
do forever;
get file (input) edit (c2) (a(1));
if c1 = c2 then
run_length = run_length + 1;
else
do; put edit (trim(run_length), c1) (a); run_length=1; end;
c1 = c2;
end;
epilog:
put edit (trim(run_length), c1) (a);
put skip;
/* The reverse of the above operation: */
declare c character (1);
declare i fixed binary;
declare new file;
open file (new) title ('/NEW.DAT,type(text),recsize(20000)');
on endfile (new) stop;
do forever;
run_length = 0;
do forever;
get file (new) edit (c) (a(1));
if index('0123456789', c) = 0 then leave;
run_length = run_length*10 + c;
end;
put edit ((c do i = 1 to run_length)) (a);
end;PowerBASIC
This version can handle any arbitrary string that doesn't contain numbers (not just letters). (A flag value could be added which would allow the inclusion of any character, but such a flag isn't in this example.)
FUNCTION RLDecode (i AS STRING) AS STRING
DIM Loop0 AS LONG, rCount AS STRING, outP AS STRING, m AS STRING
FOR Loop0 = 1 TO LEN(i)
m = MID$(i, Loop0, 1)
SELECT CASE m
CASE "0" TO "9"
rCount = rCount & m
CASE ELSE
IF LEN(rCount) THEN
outP = outP & STRING$(VAL(rCount), m)
rCount=""
ELSE
outP = outP & m
END IF
END SELECT
NEXT
FUNCTION = outP
END FUNCTION
FUNCTION RLEncode (i AS STRING) AS STRING
DIM tmp1 AS STRING, tmp2 AS STRING, outP AS STRING
DIM Loop0 AS LONG, rCount AS LONG
tmp1 = MID$(i, 1, 1)
tmp2 = tmp1
rCount = 1
FOR Loop0 = 2 TO LEN(i)
tmp1 = MID$(i, Loop0, 1)
IF tmp1 <> tmp2 THEN
outP = outP & TRIM$(STR$(rCount)) & tmp2
tmp2 = tmp1
rCount = 1
ELSE
INCR rCount
END IF
NEXT
outP = outP & TRIM$(STR$(rCount))
outP = outP & tmp2
FUNCTION = outP
END FUNCTION
FUNCTION PBMAIN () AS LONG
DIM initial AS STRING, encoded AS STRING, decoded AS STRING
initial = INPUTBOX$("Type something.")
encoded = RLEncode(initial)
decoded = RLDecode(encoded)
'in PB/Win, "?" = MSGBOX; in PB/DOS & PB/CC. "?" = PRINT
? initial & $CRLF & encoded & $CRLF & decoded
END FUNCTIONOutputs are similar to those in BASIC, above.
PowerShell
function Compress-RLE ($s) {
$re = [regex] '(.)\1*'
$ret = ""
foreach ($m in $re.Matches($s)) {
$ret += $m.Length
$ret += $m.Value[0]
}
return $ret
}
function Expand-RLE ($s) {
$re = [regex] '(\d+)(.)'
$ret = ""
foreach ($m in $re.Matches($s)) {
$ret += [string] $m.Groups[2] * [int] [string] $m.Groups[1]
}
return $ret
}Output:
PS> Compress-RLE "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" 12W1B12W3B24W1B14W PS> Expand-RLE "12W1B12W3B24W1B14W" WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Prolog
Works with SWI-Prolog.
This code is inspired from a code found here : http://groups.google.com/group/comp.lang.prolog/browse_thread/thread/b053ea2512e8b350 (author : Pascal J. Bourguignon).
% the test
run_length :-
L = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
writef('encode %s\n', [L]),
encode(L, R),
writeln(R), nl,
writef('decode %w\n', [R]),
decode(R, L1),
writeln(L1).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% encode
%
% translation
% from
% "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
% to
% "12W1B12W3B24W1B14W"
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
encode(In, Out) :-
% Because of the special management of the "strings" by Prolog
( is_list(In) -> I = In; string_to_list(In, I)),
packList(I, R1),
dcg_packList2List(R1,R2, []),
string_to_list(Out,R2).
dcg_packList2List([[N, V]|T]) -->
{ number_codes(N, LN)},
LN,
[V],
dcg_packList2List(T).
dcg_packList2List([]) --> [].
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% decode
%
% translation
% from
% "12W1B12W3B24W1B14W"
% to
% "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
decode(In, Out) :-
% Because of the special management of the "strings" by Prolog
( is_list(In) -> I = In; string_to_list(In, I)),
dcg_List2packList(I, R1, []),
packList(L1, R1),
string_to_list(Out, L1).
dcg_List2packList([H|T]) -->
{code_type(H, digit)},
parse_number([H|T], 0).
dcg_List2packList([]) --> [].
parse_number([H|T], N) -->
{code_type(H, digit), !,
N1 is N*10 + H - 48 },
parse_number(T, N1).
parse_number([H|T], N) -->
[[N, H]],
dcg_List2packList(T).
% use of library clpfd allows packList(?In, ?Out) to works
% in both ways In --> Out and In <-- Out.
:- use_module(library(clpfd)).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% ?- packList([a,a,a,b,c,c,c,d,d,e], L).
% L = [[3,a],[1,b],[3,c],[2,d],[1,e]] .
% ?- packList(R, [[3,a],[1,b],[3,c],[2,d],[1,e]]).
% R = [a,a,a,b,c,c,c,d,d,e] .
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
packList([],[]).
packList([X],[[1,X]]) :- !.
packList([X|Rest],[XRun|Packed]):-
run(X,Rest, XRun,RRest),
packList(RRest,Packed).
run(Var,[],[1,Var],[]).
run(Var,[Var|LRest],[N1, Var],RRest):-
N #> 0,
N1 #= N + 1,
run(Var,LRest,[N, Var],RRest).
run(Var,[Other|RRest], [1,Var],[Other|RRest]):-
dif(Var,Other).Output :
?- run_length. encode WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W decode 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW true .
Pure
using system;
encode s = strcat $ map (sprintf "%d%s") $ encode $ chars s with
encode [] = [];
encode xs@(x:_) = (#takewhile (==x) xs,x) : encode (dropwhile (==x) xs);
end;
decode s = strcat [c | n,c = parse s; i = 1..n] with
parse s::string = regexg item "([0-9]+)(.)" REG_EXTENDED s 0;
item info = val (reg 1 info!1), reg 2 info!1;
end;
let s = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
let r = encode s; // "12W1B12W3B24W1B14W"
decode r;PureBasic
with some optimations to use pointers instead of string functions. According to the task description it works with uppercase A - Z. In this implementation it also functions with all characters that are non-digits and whose value is non-zero.
Procedure.s RLDecode(toDecode.s)
Protected.s repCount, output, currChar, tmp
Protected *c.Character = @toDecode
While *c\c <> #Null
currChar = Chr(*c\c)
Select *c\c
Case '0' To '9'
repCount + currChar
Default
If repCount
tmp = Space(Val(repCount))
ReplaceString(tmp, " ", currChar, #PB_String_InPlace)
output + tmp
repCount = ""
Else
output + currChar
EndIf
EndSelect
*c + SizeOf(Character)
Wend
ProcedureReturn output
EndProcedure
Procedure.s RLEncode(toEncode.s)
Protected.s currChar, prevChar, output
Protected repCount
Protected *c.Character = @toEncode
prevChar = Chr(*c\c)
repCount = 1
*c + SizeOf(Character)
While *c\c <> #Null
currChar = Chr(*c\c)
If currChar <> prevChar
output + Str(repCount) + prevChar
prevChar = currChar
repCount = 1
Else
repCount + 1
EndIf
*c + SizeOf(Character)
Wend
output + Str(repCount)
output + prevChar
ProcedureReturn output
EndProcedure
If OpenConsole()
Define initial.s, encoded.s, decoded.s
Print("Type something: ")
initial = Input()
encoded = RLEncode(initial)
decoded = RLDecode(encoded)
PrintN(initial)
PrintN(RLEncode(initial))
PrintN(RLDecode(encoded))
Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")
Input()
CloseConsole()
EndIfSample output:
Type something: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWW WWW WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Python
def encode(input_string):
count = 1
prev = None
lst = []
for character in input_string:
if character != prev:
if prev:
entry = (prev, count)
lst.append(entry)
count = 1
prev = character
else:
count += 1
else:
try:
entry = (character, count)
lst.append(entry)
return (lst, 0)
except Exception as e:
print("Exception encountered {e}".format(e=e))
return (e, 1)
def decode(lst):
q = []
for character, count in lst:
q.append(character * count)
return ''.join(q)
#Method call
value = encode("aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa")
if value[1] == 0:
print("Encoded value is {}".format(value[0]))
decode(value[0])Functional
from itertools import groupby
def encode(input_string):
return [(len(list(g)), k) for k,g in groupby(input_string)]
def decode(lst):
return ''.join(c * n for n,c in lst)
encode("aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa")
decode([(5, 'a'), (6, 'h'), (7, 'm'), (1, 'u'), (7, 'i'), (6, 'a')])
By regular expression
The simplified input range of only uppercase characters allows a simple regular expression to be applied repeatedly for encoding, and another for decoding:
from re import sub
def encode(text):
'''
Doctest:
>>> encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW')
'12W1B12W3B24W1B14W'
'''
return sub(r'(.)\1*', lambda m: str(len(m.group(0))) + m.group(1),
text)
def decode(text):
'''
Doctest:
>>> decode('12W1B12W3B24W1B14W')
'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
'''
return sub(r'(\d+)(\D)', lambda m: m.group(2) * int(m.group(1)),
text)
textin = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
assert decode(encode(textin)) == textinQuackery
lookandsay is defined at Look-and-say sequence#Quackery.
[ lookandsay ] is encode ( $ --> $ )
[ $ "" 0 rot
witheach
[ dup
char 0 char 9 1+
within iff
[ char 0 -
swap 10 * + ]
else
[ swap of join
0 ] ]
drop ] is decode ( $ --> $ )
$ "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
dup echo$ cr
encode
dup echo$ cr
decode
echo$ cr- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
R
R has a built-in function, rle, for run length encoding. This modification allows input and output in the forms specified above.
runlengthencoding <- function(x)
{
splitx <- unlist(strsplit(input, ""))
rlex <- rle(splitx)
paste(with(rlex, as.vector(rbind(lengths, values))), collapse="")
}
input <- "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
runlengthencoding(input)Similarly, inverse.rle provides decompression after a run length encoding.
inverserunlengthencoding <- function(x)
{
lengths <- as.numeric(unlist(strsplit(output, "[[:alpha:]]")))
values <- unlist(strsplit(output, "[[:digit:]]"))
values <- values[values != ""]
uncompressed <- inverse.rle(list(lengths=lengths, values=values))
paste(uncompressed, collapse="")
}
output <- "12W1B12W3B24W1B14W"
inverserunlengthencoding(output)Racket
#lang racket
(define (encode str)
(regexp-replace* #px"(.)\\1*" str (λ (m c) (~a (string-length m) c))))
(define (decode str)
(regexp-replace* #px"([0-9]+)(.)" str (λ (m n c) (make-string (string->number n) (string-ref c 0)))))Raku
(formerly Perl 6) Note that Raku regexes don't care about unquoted whitespace, and that backrefs count from 0, not from 1.
sub encode($str) { $str.subst(/(.) $0*/, { $/.chars ~ $0 }, :g) }
sub decode($str) { $str.subst(/(\d+) (.)/, { $1 x $0 }, :g) }
my $e = encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW');
say $e;
say decode($e);Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
REXX
version 1
The task (input) rule was relaxed a bit as this program accepts upper─ and lowercase input.
An error message is generated if the input text is invalid.
In addition, a yay or nay message is also displayed if the decoding of the encoding was successful.
Note that this REXX version (for encoding and decoding) uses a replication count, not the count of characters,
so a replication count of 11 represents a count of 12 characters.
/*REXX program encodes and displays a string by using a run─length encoding scheme. */
parse arg input . /*normally, input would be in a file. */
default= 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
if input=='' | input=="," then input= default /*Not specified? Then use the default.*/
encode= RLE(input) ; say ' input=' input /*encode input string; display input. */
say 'encoded=' encode /* display run─len*/
decode= RLD(encode); say 'decoded=' decode /*decode the run─len; display decode.*/
if decode==input then say 'OK'; else say "¬ OK" /*display yay or nay (success/failure).*/
exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
err: say; say "***error*** input data isn't alphabetic:" c; say; exit 13
/*──────────────────────────────────────────────────────────────────────────────────────*/
RLE: procedure; parse arg x; $= /*$: is the output string (so far). */
Lx= length(x) /*get length of the plain text string. */
do j=1 by 0 to Lx; c= substr(x, j, 1) /*obtain a character from plain text. */
if \datatype(c, 'M') then call err /*Character not a letter? Issue error.*/
r= 0 /*R: is NOT the number of characters. */
do k=j+1 to Lx while substr(x, k, 1)==c /*while characters ≡ C */
r= r + 1 /*bump the replication count for a char*/
end /*k*/
j= j + r + 1 /*increment (add to) the DO loop index.*/
if r==0 then $= $ || c /*don't use R if it is equal to zero.*/
else $= $ || r || c /*add character to the encoded string. */
end /*j*/; return $ /*return the encoded string to caller. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
RLD: procedure; parse arg x; $= /*$: is the output string (so far). */
Lx= length(x) /*get the length of the encoded string.*/
do j=1 by 0 to Lx; c= substr(x, j, 1) /*obtain a character from run encoding.*/
if \datatype(c, 'W') then do; $= $ || c; j= j + 1; iterate /*j*/
end /* [↑] a loner char, add it to output.*/
#= 1 /* [↓] W: use a Whole number*/
do k=j+1 to Lx while datatype(substr(x,k,1), 'w') /*while numeric*/
#= # + 1 /*bump the count of the numeric chars. */
end /*k*/
n= substr(x, j, #) + 1 /*#: the length of encoded character. */
$= $ || copies( substr(x, k, 1), n) /*N: is now the number of characters. */
j= j + # + 1 /*increment the DO loop index by D+1. */
end /*j*/; return $ /*return the decoded string to caller. */- output when using the default input:
input= WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded= 11WB11W2B23WB13W decoded= WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
version 2
/*REXX*/
s='WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
Say ' s='s
enc=encode(s)
Say 'enc='enc
dec=decode(enc)
Say 'dec='dec
if dec==s Then Say 'OK'
Exit
encode: Procedure
Parse Arg s
c=left(s,1)
cnt=1
ol=''
Do i=2 To length(s)
If substr(s,i,1)=c Then
cnt=cnt+1
Else Do
Call o cnt||c
c=substr(s,i,1)
cnt=1
End
End
Call o cnt||c
Return ol
decode: Procedure
Parse Arg s
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
ol=''
Do While s<>''
p=verify(s,abc,'M')
Parse Var s cnt =(p) c +1 s
Call o copies(c,cnt)
End
Return ol
o: ol=ol||arg(1)
Return- Output:
s=WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW enc=12W1B12W3B24W1B14W dec=WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW OK
version 3
No need to output counts that are 1
/*REXX*/
s='WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
Say ' s='s
enc=encode(s)
Say 'enc='enc
dec=decode(enc)
Say 'dec='dec
if dec==s Then Say 'OK'
Exit
encode: Procedure
Parse Arg s
c=left(s,1)
cnt=1
ol=''
Do i=2 To length(s)
If substr(s,i,1)=c Then
cnt=cnt+1
Else Do
If cnt=1 Then
Call o c
Else
Call o cnt||c
c=substr(s,i,1)
cnt=1
End
End
Call o cnt||c
Return ol
decode: Procedure
Parse Arg s
abc='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
ol=''
Do While s<>''
p=verify(s,abc,'M')
If pos(left(s,1),abc)>0 Then Do
Parse Var s c +1 s
Call o c
End
Else Do
Parse Var s cnt =(p) c +1 s
Call o copies(c,cnt)
End
End
Return ol
o: ol=ol||arg(1)
Return- Output:
s=WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW enc=12WB12W3B24WB14W dec=WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW OK
Ring
# Project : Run-length encoding
load "stdlib.ring"
test = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
num = 0
nr = 0
decode = newlist(7,2)
for n = 1 to len(test) - 1
if test[n] = test[n+1]
num = num + 1
else
nr = nr + 1
decode[nr][1] = (num + 1)
decode[nr][2] = test[n]
see "" + (num + 1) + test[n]
num = 0
ok
next
see "" + (num + 1) + test[n]
see nl
nr = nr + 1
decode[nr][1] = (num + 1)
decode[nr][2] = test[n]
for n = 1 to len(decode)
dec = copy(decode[n][2], decode[n][1])
see dec
nextOutput:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
RPL
≪ DUP 1 DUP SUB → in c
≪ "" 1
2 in SIZE FOR j
in j DUP SUB
IF DUP c == THEN DROP 1 +
ELSE
ROT ROT
→STR + c +
SWAP 'c' STO 1
END
NEXT
→STR + c +
≫ ≫ ‘RLENC’ STO
≪ → in
≪ "" 0
1 in SIZE FOR j
in j DUP SUB
IF DUP "A" ≥ THEN
ROT 1 4 ROLL START OVER + NEXT
SWAP DROP 0
ELSE STR→ SWAP 10 * + END
NEXT DROP
≫ ≫ ‘RLDEC’ STO
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" RLENC DUP RLDEC
- Output:
2: "12W1B12W3B24W1B14W" 1: "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
Ruby
Built-in
Ruby has built-in run-length encoding in the form of chunk, here I provide a thin wrapper around it:
# run_encode("aaabbbbc") #=> [["a", 3], ["b", 4], ["c", 1]]
def run_encode(string)
string
.chars
.chunk{|i| i}
.map {|kind, array| [kind, array.length]}
end
# run_decode([["a", 3], ["b", 4], ["c", 1]]) #=> "aaabbbbc"
def run_decode(char_counts)
char_counts
.map{|char, count| char * count}
.join
enddef encode(string)
string.scan(/(.)(\1*)/).collect do |char, repeat|
[1 + repeat.length, char]
end.join
end
def decode(string)
string.scan(/(\d+)(\D)/).collect {|length, char| char * length.to_i}.join
endThis usage also seems to be idiomatic, and perhaps less cryptic:
def encode(string)
string.scan(/(.)(\1*)/).inject("") do |encoding, (char, repeat)|
encoding << (1 + repeat.length).to_s << char
end
end
def decode(string)
string.scan(/(\d+)(\D)/).inject("") do |decoding, (length, char)|
decoding << char * length.to_i
end
end
By regular expression
The simplified input range of only uppercase characters allows a simple regular expression to be applied repeatedly for encoding, and another for decoding:
def encode(str)
str.gsub(/(.)\1*/) {$&.length.to_s + $1}
end
def decode(str)
str.gsub(/(\d+)(\D)/) {$2 * $1.to_i}
endTest:
orig = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
p enc = encode(orig)
p dec = decode(enc)
puts "success!" if dec == orig- Output:
"12W1B12W3B24W1B14W" "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" success!
Run BASIC
string$ = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
beg = 1
i = 1
[loop]
s$ = mid$(string$,beg,1)
while mid$(string$,i,1) = s$
i = i + 1
wend
press$ = press$ ; i-beg;s$
beg = i
if i < len(string$) then goto [loop]
print "Compressed:";press$
beg = 1
i = 1
[expand]
while mid$(press$,i,1) <= "9"
i = i + 1
wend
for j = 1 to val(mid$(press$,beg, i - beg))
expand$ = expand$ + mid$(press$,i,1)
next j
i = i + 1
beg = i
if i < len(press$) then goto [expand]
print " Expanded:";expand$Output:
Compressed:12W1B12W3B24W1B14W Expanded:WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Rust
fn encode(s: &str) -> String {
s.chars()
// wrap all values in Option::Some
.map(Some)
// add an Option::None onto the iterator to clean the pipeline at the end
.chain(std::iter::once(None))
.scan((0usize, '\0'), |(n, c), elem| match elem {
Some(elem) if *n == 0 || *c == elem => {
// the run continues or starts here
*n += 1;
*c = elem;
// this will not have an effect on the final string because it is empty
Some(String::new())
}
Some(elem) => {
// the run ends here
let run = format!("{}{}", n, c);
*n = 1;
*c = elem;
Some(run)
}
None => {
// the string ends here
Some(format!("{}{}", n, c))
}
})
// concatenate together all subresults
.collect()
}
fn decode(s: &str) -> String {
s.chars()
.fold((0usize, String::new()), |(n, text), c| {
if c.is_ascii_digit() {
// some simple number parsing
(
n * 10 + c.to_digit(10).expect("invalid encoding") as usize,
text,
)
} else {
// this must be the character that is repeated
(0, text + &format!("{}", c.to_string().repeat(n)))
}
})
.1
}
fn main() {
let text = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
let encoded = encode(text);
let decoded = decode(&encoded);
println!("original: {}\n encoded: {}\n decoded: {}", text, encoded, decoded);
assert_eq!(text, decoded);
}- Output:
original: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW encoded: 12W1B12W3B24W1B14W decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Scala
Care is taken to use StringBuilder for performance reasons.
def encode(s: String) = (1 until s.size).foldLeft((1, s(0), new StringBuilder)) {
case ((len, c, sb), index) if c != s(index) => sb.append(len); sb.append(c); (1, s(index), sb)
case ((len, c, sb), _) => (len + 1, c, sb)
} match {
case (len, c, sb) => sb.append(len); sb.append(c); sb.toString
}
def decode(s: String) = {
val sb = new StringBuilder
val Code = """(\d+)([A-Z])""".r
for (Code(len, c) <- Code findAllIn s) sb.append(c * len.toInt)
sb.toString
}A simpler (?) encoder:
def encode(s:String) = {
s.foldLeft((0,s(0),""))( (t,c) => t match {case (i,p,s) => if (p==c) (i+1,p,s) else (1,c,s+i+p)})
match {case (i,p,s) => s+i+p}
}To make it faster (it's also faster than the longer implementation above) just replace "" with new StringBuilder and s+i+p with {s.append(i);s.append(p)}
A simpler (?) decoder (that can handle a string like "2AB", producing "AAB"):
def decode(s: String, Code: scala.util.matching.Regex = """(\d+)?([a-zA-Z])""".r) =
Code.findAllIn(s).foldLeft("") { case (acc, Code(len, c)) =>
acc + c * Option(len).map(_.toInt).getOrElse(1)
}Scheme
(define (run-length-decode v)
(apply string-append (map (lambda (p) (make-string (car p) (cdr p))) v)))
(define (run-length-encode s)
(let ((n (string-length s)))
(let loop ((i (- n 2)) (c (string-ref s (- n 1))) (k 1) (v '()))
(if (negative? i) (cons (cons k c) v)
(let ((x (string-ref s i)))
(if (char=? c x) (loop (- i 1) c (+ k 1) v)
(loop (- i 1) x 1 (cons (cons k c) v))))))))
(run-length-encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
; ((12 . #\W) (1 . #\B) (12 . #\W) (3 . #\B) (24 . #\W) (1 . #\B) (14 . #\W))
(run-length-decode '((12 . #\W) (1 . #\B) (12 . #\W) (3 . #\B) (24 . #\W) (1 . #\B) (14 . #\W)))
; "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"sed
The encode script:
/^$/ b
:start
/^[0-9]/ b
s/^/1/
:loop
h
/^9+([^0-9])\1+/ {
s/^(9+).*/0\1/
y/09/10/
G
s/^(.+)\n[0-9]+.(.*)/\1\2/
b loop }
/^[0-9]*[0-8]([^0-9])\1+/ {
s/^[0-9]*([0-8]).*/\1/
y/012345678/123456789/
G
s/^(.)\n([0-9]*)[0-8].(.*)/\2\1\3/
b loop }
/^[0-9]+9+([^0-9])\1+/ {
s/^[0-9]*([0-8]9+).*/\1/
y/0123456789/1234567890/
G
s/^(.+)\n([0-9]*)[0-8]9+.(.*)/\2\1\3/
b loop }
s/^([0-9]+.)(.*)/\2\1/
b startThe decode script:
/^$/ b
:start
/^[^0-9]/ b
:loop
/^1[^0-9]/ {
s/^1(.)(\1*)(.*)/\3\1\2/
b start }
h
/^[0-9]*[1-9][^0-9]/ {
s/^[0-9]*([1-9]).*/\1/
y/123456789/012345678/
G
s/^([0-8])\n([0-9]*)[1-9]([^0-9])(.*)/\2\1\3\3\4/
b loop }
/^[0-9]+0[^0-9]/ {
s/^[0-9]*([1-9]0+)[^0-9].*/\1/
y/0123456789/9012345678/
G
s/^([0-9]+)\n([0-9]*)[1-9]0+([^0-9])(.*)/\2\1\3\3\4/
s/^0+//
b loop }Example (assuming the scripts reside in the files encode.sed and decode.sed):
sed -rf encode.sed <<< "foo oops"
# 1f2o1 2o1p1s
sed -rf decode.sed <<< "1f2o1 2o1p1s"
# foo oops
(sed -rf decode.sed | sed -rf encode.sed) <<< 1000.
# 1000.Seed7
$ include "seed7_05.s7i";
include "scanstri.s7i";
const func string: letterRleEncode (in string: data) is func
result
var string: result is "";
local
var char: code is ' ';
var integer: index is 1;
begin
if length(data) <> 0 then
code := data[1];
repeat
incr(index);
until index > length(data) or code <> data[index];
result := str(pred(index)) & str(code) & letterRleEncode(data[index ..]);
end if;
end func;
const func string: letterRleDecode (in var string: data) is func
result
var string: result is "";
local
var integer: count is 0;
begin
if length(data) <> 0 then
count := integer parse getDigits(data);
result := data[1 len 1] mult count & letterRleDecode(data[2 ..]);
end if;
end func;
const proc: main is func
begin
writeln(letterRleEncode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"));
writeln(letterRleDecode("12W1B12W3B24W1B14W"));
end func;SETL
program rle;
test := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
print("Input:");
print(test);
print("Encoded:");
print(enc := rlencode(test));
print("Decoded:");
print(rldecode(enc));
proc rlencode(s);
loop while s /= "" do
part := span(s, s(1));
r +:= str #part + part(1);
end loop;
return r;
end proc;
proc rldecode(s);
loop while s /= "" do
num := span(s, "0123456789");
item := notany(s, "");
r +:= val num * item;
end loop;
return r;
end proc;
end program;- Output:
Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded: 12W1B12W3B24W1B14W Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Sidef
First solution:
func encode(str) {
str.gsub(/((.)(\2*))/, {|a,b| "#{a.len}#{b}" });
}
func decode(str) {
str.gsub(/(\d+)(.)/, {|a,b| b * a.to_i });
}- Output:
12W1B12W3B24W1B14W
Second solution, encoding the length into a byte:
func encode(str) {
str.gsub(/(.)(\1{0,254})/, {|a,b| b.len+1 -> chr + a});
}
func decode(str) {
var chars = str.chars;
var r = '';
(chars.len/2 -> int).range.each { |i|
r += (chars[2*i + 1] * chars[2*i].ord);
}
return r;
}- Output:
"\fW\1B\fW\3B\30W\1B\16W"
Smalltalk
See Run-length encoding/Smalltalk
A "functional" version without RunArray:
(and others)
|compress decompress|
compress := [:string |
String streamContents:[:out |
|count prev|
count := 0.
(string,'*') "trick to avoid final run handling in loop"
inject:nil
into:[:prevChar :ch |
ch ~= prevChar ifTrue:[
count = 0 ifFalse:[
count printOn:out.
out nextPut:prevChar.
count := 0.
].
].
count := count + 1.
ch
]
]
].
decompress := [:string |
String streamContents:[:out |
string readingStreamDo:[:in |
[in atEnd] whileFalse:[
|n ch|
n := Integer readFrom:in.
ch := in next.
out next:n put:ch.
]
]
].
].compress value:'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
-> '12W1B12W3B24W1B14W'
decompress value:'12W1B12W3B24W1B14W'
-> 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'Most Smalltalk dialects include a class named "RunArray", which can be used as:
compress := [:string |
String streamContents:[:out |
string asRunArray runsDo:[:count :char |
count printOn:out. out nextPut:char]]].SNOBOL4
* # Encode RLE
define('rle(str)c,n') :(rle_end)
rle str len(1) . c :f(return)
str span(c) @n =
rle = rle n c :(rle)
rle_end
* # Decode RLE
define('elr(str)c,n') :(elr_end)
elr str span('0123456789') . n len(1) . c = :f(return)
elr = elr dupl(c,n) :(elr)
elr_end
* # Test and display
str = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
output = str;
str = rle(str); output = str
str = elr(str); output = str
endOutput:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
SparForte
As a structured script.
#!/usr/local/bin/spar
pragma is
annotate( summary, "rle" );
annotate( description, "Given a string containing uppercase characters (A-Z)," );
annotate( description, "compress repeated 'runs' of the same character by" );
annotate( description, "storing the length of that run, and provide a function to" );
annotate( description, "reverse the compression. The output can be anything, as" );
annotate( description, "long as you can recreate the input with it." );
annotate( description, "" );
annotate( description, "Example:" );
annotate( description, "Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" );
annotate( description, "Output: 12W1B12W3B24W1B14W" );
annotate( see_also, "http://rosettacode.org/wiki/Run-length_encoding" );
annotate( author, "Ken O. Burtch" );
license( unrestricted );
restriction( no_external_commands );
end pragma;
procedure rle is
function to_rle( s : string ) return string is
begin
if strings.length( s ) = 0 then
return "";
end if;
declare
result : string;
code : character;
prefix : string;
first : natural := 1;
index : natural := 1;
begin
while index <= strings.length( s ) loop
first := index;
index := @+1;
code := strings.element( s, positive(first) );
while index <= strings.length( s ) loop
exit when code /= strings.element( s, positive(index) );
index := @+1;
exit when index-first = 99;
end loop;
prefix := strings.trim( strings.image( index - first ), trim_end.left );
result := @ & prefix & code;
end loop;
return result;
end;
end to_rle;
function from_rle( s : string ) return string is
begin
if strings.length( s ) = 0 then
return "";
end if;
declare
result : string;
index : positive := 1;
prefix : string;
code : character;
begin
loop
prefix := "" & strings.element( s, index );
index := @+1;
if strings.is_digit( strings.element( s, index ) ) then
prefix := @ & strings.element( s, index );
index := @+1;
end if;
code := strings.element( s, index );
index := @+1;
result := @ & ( numerics.value( prefix ) * code );
exit when natural(index) > strings.length( s );
end loop;
return result;
end;
end from_rle;
begin
? to_rle( "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" );
? from_rle( "12W1B12W3B24W1B14W");
end rle;SQL
- RLE encoding
-- variable table
drop table if exists var;
create temp table var ( value varchar(1000) );
insert into var(value) select 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW';
-- select
with recursive
ints(num) as
(
select 1
union all
select num+1
from ints
where num+1 <= length((select value from var))
)
,
chars(num,chr,nextChr,isGroupEnd) as
(
select tmp.*, case when tmp.nextChr <> tmp.chr then 1 else 0 end groupEnds
from (
select num,
substring((select value from var), num, 1) chr,
(select substring((select value from var), num+1, 1)) nextChr
from ints
) tmp
)
select (select value from var) plain_text, (
select string_agg(concat(cast(maxNoWithinGroup as varchar(10)) , chr), '' order by num)
from (
select *, max(noWithinGroup) over (partition by chr, groupNo) maxNoWithinGroup
from (
select num,
chr,
groupNo,
row_number() over( partition by chr, groupNo order by num) noWithinGroup
from (
select *, (select count(*)
from chars chars2
where chars2.isGroupEnd = 1 and
chars2.chr = chars.chr and
chars2.num < chars.num) groupNo
from chars
) tmp
) sub
) final
where noWithinGroup = 1
) Rle_Compressed- RLE decoding
-- variable table
DROP TABLE IF EXISTS var;
CREATE temp TABLE var ( VALUE VARCHAR(1000) );
INSERT INTO var(VALUE) SELECT '1A2B3C4D5E6F';
-- select
WITH recursive
ints(num) AS
(
SELECT 1
UNION ALL
SELECT num+1
FROM ints
WHERE num+1 <= LENGTH((SELECT VALUE FROM var))
)
,
chars(num,chr,nextChr) AS
(
SELECT tmp.*
FROM (
SELECT num,
SUBSTRING((SELECT VALUE FROM var), num, 1) chr,
(SELECT SUBSTRING((SELECT VALUE FROM var), num+1, 1)) nextChr
FROM ints
) tmp
)
,
charsWithGroup(num,chr,nextChr,group_no) AS
(
SELECT *,(SELECT COUNT(*)
FROM chars chars2
WHERE chars2.chr !~ '[0-9]' AND
chars2.num < chars.num) group_No
FROM chars
)
,
charsWithGroupAndLetter(num,chr,nextChr,group_no,group_letter) AS
(
SELECT *,(SELECT chr
FROM charsWithGroup g2
where g2.group_no = charsWithGroup.group_no
ORDER BY num DESC
LIMIT 1)
FROM charsWithGroup
)
,
lettersWithCount(group_no,amount,group_letter) AS
(
SELECT group_no, string_agg(chr, '' ORDER BY num), group_letter
FROM charsWithGroupAndLetter
WHERE chr ~ '[0-9]'
GROUP BY group_no, group_letter
)
,
lettersReplicated(group_no,amount,group_letter, replicated_Letter) AS
(
SELECT *, rpad(group_letter, cast(amount as int), group_letter)
FROM lettersWithCount
)
select (SELECT value FROM var) rle_encoded,
string_agg(replicated_Letter, '' ORDER BY group_no) decoded_string
FROM lettersReplicatedStandard ML
fun encode str =
let
fun aux (sub, acc) =
case Substring.getc sub
of NONE => rev acc
| SOME (x, sub') =>
let
val (y, z) = Substring.splitl (fn c => c = x) sub'
in
aux (z, (x, Substring.size y + 1) :: acc)
end
in
aux (Substring.full str, [])
end
fun decode lst =
concat (map (fn (c,n) => implode (List.tabulate (n, fn _ => c))) lst)Example:
- encode "aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa"; val it = [(#"a",5),(#"h",6),(#"m",7),(#"u",1),(#"i",7),(#"a",6)] : (char * int) list - decode [(#"a",5),(#"h",6),(#"m",7),(#"u",1),(#"i",7),(#"a",6)]; val it = "aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa" : string
Swift
Using array as the internal representation of the encoded input:
import Foundation
// "WWWBWW" -> [(3, W), (1, B), (2, W)]
func encode(input: String) -> [(Int, Character)] {
return input.characters.reduce([(Int, Character)]()) {
if $0.last?.1 == $1 { var r = $0; r[r.count - 1].0++; return r }
return $0 + [(1, $1)]
}
}
// [(3, W), (1, B), (2, W)] -> "WWWBWW"
func decode(encoded: [(Int, Character)]) -> String {
return encoded.reduce("") { $0 + String(count: $1.0, repeatedValue: $1.1) }
}Usage:
let input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
let output = decode(encode(input))
print(output == input)- Output:
true
Converting encoded array into the string and then decoding it using NSScanner:
// "3W1B2W" -> "WWWBWW"
func decode(encoded: String) -> String {
let scanner = NSScanner(string: encoded)
var char: NSString? = nil
var count: Int = 0
var out = ""
while scanner.scanInteger(&count) {
while scanner.scanCharactersFromSet(NSCharacterSet.letterCharacterSet(), intoString: &char) {
out += String(count: count, repeatedValue: Character(char as! String))
}
}
return out
}let encodedString = encode(input).reduce("") { $0 + "\($1.0)\($1.1)" }
print(encodedString)
let outputString = decode(encodedString)
print(outputString == input)- Output:
12W1B12W3B24W1B14W true
Tcl
The encoding is an even-length list with elements {count char ...}
proc encode {string} {
set encoding {}
# use a regular expression to match runs of one character
foreach {run -} [regexp -all -inline {(.)\1+|.} $string] {
lappend encoding [string length $run] [string index $run 0]
}
return $encoding
}
proc decode {encoding} {
foreach {count char} $encoding {
append decoded [string repeat $char $count]
}
return $decoded
}set str "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
set enc [encode $str] ;# ==> {12 W 1 B 12 W 3 B 24 W 1 B 14 W}
set dec [decode $enc]
if {$str eq $dec} {
puts "success"
}TMG
Unix TMG is designed to process and generate files rather than process text in memory. Therefore encoding and decoding parts can be done in separate programs.
Encoding:
loop: ordcop [lch?]\loop;
ordcop: ord/copy;
ord: char(ch)/last [ch!=lch?]\new [cnt++] fail;
new: ( [lch?] parse(out) | () ) [lch=ch] [cnt=1] fail;
out: decimal(cnt) scopy = { 2 1 };
last: parse(out) [lch=0];
copy: smark any(!<<>>);
ch: 0;
lch: 0;
cnt: 0;Decoding:
loop: readint(n) copy\loop;
copy: smark any(!<<>>)
repeat: [n?] parse(( scopy )) [--n>0?]\repeat;
/* Reads decimal integer */
readint: proc(n;i) ignore(<<>>) [n=0] inta
int1: [n = n*12+i] inta\int1;
inta: char(i) [i<72?] [(i =- 60)>=0?];
i: 0;
n: 0;TSE SAL
STRING PROC FNStringGetDecodeStringCharacterEqualCountS( STRING inS )
STRING s1[255] = ""
STRING s2[255] = ""
STRING s3[255] = ""
STRING s4[255] = ""
INTEGER I = 0
INTEGER J = 0
INTEGER K = 0
INTEGER L = 0
K = Length( inS )
I = 1 - 1
REPEAT
J = 1 - 1
s3 = ""
REPEAT
I = I + 1
J = J + 1
s1 = SubStr( inS, I, 1 )
s3 = s3 + s1
s4 = SubStr( inS, I + 1, 1 )
UNTIL ( NOT ( s4 IN '0'..'9' ) )
FOR L = 1 TO Val( s3 )
s2 = s2 + s4
ENDFOR
I = I + 1
UNTIL ( I >= ( K - 1 ) )
RETURN( s2 )
END
//
STRING PROC FNStringGetEncodeStringCharacterEqualCountS( STRING inS )
STRING s1[255] = ""
STRING s2[255] = ""
INTEGER I = 0
INTEGER J = 0
INTEGER K = 0
K = Length( inS )
I = 1 - 1
REPEAT
J = 1 - 1
REPEAT
I = I + 1
J = J + 1
s1 = SubStr( inS, I, 1 )
UNTIL ( NOT ( SubStr( inS, I + 1, 1 ) == s1 ) )
s2 = s2 + Str( J ) + s1
UNTIL ( I >= ( K - 1 ) )
RETURN( s2 )
END
//
STRING PROC FNStringGetEncodeDecodeStringCharacterEqualCountS( STRING inS )
STRING s1[255] = FNStringGetEncodeStringCharacterEqualCountS( inS )
STRING s2[255] = FNStringGetDecodeStringCharacterEqualCountS( s1 )
RETURN( s2 )
END
//
PROC Main()
STRING s1[255] = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
STRING s2[255] = ""
IF ( NOT ( Ask( "string: get: encode: decode: string: character: equal: count: inS = ", s1, _EDIT_HISTORY_ ) ) AND ( Length( s1 ) > 0 ) ) RETURN() ENDIF
s2 = FNStringGetEncodeDecodeStringCharacterEqualCountS( s1 )
Warn( "equal strings if result is 1", ",", " ", "and the result is", ":", " ", s1 == s2 )
ENDTUSCRIPT
$$ MODE TUSCRIPT,{}
input="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",output=""
string=strings(input," ? ")
letter=ACCUMULATE(string,freq)
freq=SPLIT(freq),letter=SPLIT(letter)
output=JOIN(freq,"",letter)
output=JOIN(output,"")
PRINT input
PRINT outputOutput:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W
Uiua
# Run Length Encoding and Decoding
Rle ← setinv(
/◇⊂⍚⊂°⋕°▽
| ▽⊃⊜⋕(♭⊜∘¬)⊸∈+@0⇡10)
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
&p⨬("oops"|"good")≍&p.°Rle&p.⊸Rle&p.- Output:
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW 12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW good
UNIX Shell
encode() {
local phrase=$1
[[ -z $phrase ]] && return
local result="" count=0 char=${phrase:0:1}
for ((i = 0; i < ${#phrase}; i++)); do
if [[ ${phrase:i:1} == "$char" ]]; then
((count++))
else
result+="$(encode_sequence "$count" "$char")"
char=${phrase:i:1}
count=1
fi
done
result+="$(encode_sequence "$count" "$char")"
echo "$result"
}
encode_sequence() {
local count=$1 char=$2
((count == 1)) && count=""
echo "${count}${char}"
}
decode() {
local phrase=$1
local result=""
local count char
while [[ $phrase =~ ([[:digit:]]+)([^[:digit:]]) ]]; do
printf -v phrase "%s%s%s" \
"${phrase%%${BASH_REMATCH[0]}*}" \
"$(repeat "${BASH_REMATCH[1]}" "${BASH_REMATCH[2]}")" \
"${phrase#*${BASH_REMATCH[0]}}"
done
echo "$phrase"
}
repeat() {
local count=$1 char=$2
local result
# string of count spaces
printf -v result "%*s" "$count" ""
# replace spaces with the char
echo "${result// /$char}"
}Demo
str="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
enc=$(encode "$str")
dec=$(decode "$enc")
declare -p str enc dec
[[ $str == "$dec" ]] && echo success || echo failureOutput
declare -- str="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" declare -- enc="12WB12W3B24WB14W" declare -- dec="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW" success
Ursala
A standard library function, rlc, does most of the work for this task, which is a second order function taking a binary predicate that decides when consecutive items of an input list belong to the same run.
#import std
#import nat
encode = (rlc ==); *= ^lhPrNCT\~&h %nP+ length
decode = (rlc ~&l-=digits); *=zyNCXS ^|DlS/~& iota+ %np
test_data = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW'
#show+
example =
<
encode test_data,
decode encode test_data>The output shows an encoding of the test data, and a decoding of the encoding, which matches the original test data.
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
VBA
Option Explicit
Sub Main()
Dim p As String
p = length_encoding("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
Debug.Print p
Debug.Print length_decoding(p)
End Sub
Private Function length_encoding(S As String) As String
Dim F As String, r As String, a As String, n As Long, c As Long, k As Long
r = Left(S, 1)
c = 1
For n = 2 To Len(S)
If r <> Mid(S, n, 1) Then
a = a & c & r
r = Mid(S, n, 1)
c = 1
Else
c = c + 1
End If
Next
length_encoding = a & c & r
End Function
Private Function length_decoding(S As String) As String
Dim F As Long, r As String, a As String
For F = 1 To Len(S)
If IsNumeric(Mid(S, F, 1)) Then
r = r & Mid(S, F, 1)
Else
a = a & String(CLng(r), Mid(S, F, 1))
r = vbNullString
End If
Next
length_decoding = a
End Function- Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Vedit macro language
The following example encodes/decodes an entire file. Each run is coded with two bytes. The first byte is the run length with high bit set, the second byte is the character code. ASCII characters with run length of 1 are left unchanged. Character codes above 127 are always coded with run length. Newlines are not converted (the regular expression does not count newlines). This methods supports any type of input.
:RL_ENCODE:
BOF
While (!At_EOF) {
if (At_EOL) { Line(1) Continue } // skip newlines
#1 = Cur_Char // #1 = character
Match("(.)\1*", REGEXP) // count run length
#2 = Chars_Matched // #2 = run length
if (#2 > 127) { #2 = 127 } // can be max 127
if (#2 > 1 || #1 > 127) {
Del_Char(#2)
Ins_Char(#2 | 128) // run length (high bit set)
Ins_Char(#1) // character
} else { // single ASCII char
Char // skip
}
}
Return
:RL_DECODE:
BOF
While (!At_EOF) {
#2 = Cur_Char
if (#2 > 127) { // is this run length?
#1 = Cur_Char(1) // #1 = character value
Del_Char(2)
Ins_Char(#1, COUNT, #2 & 127)
} else { // single ASCII char
Char
}
}
ReturnV (Vlang)
const test = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
fn main() {
encoded := encode(test)
println(encoded)
println(decode(encoded))
}
fn encode(data string) string {
mut encode :=""
mut temp := []u8{}
for key, value in data {
if key > 1 && value != data[key - 1] {
encode += temp.len.str() + temp[0].ascii_str()
temp.clear()
}
temp << value
}
encode += temp.len.str() + temp[0].ascii_str()
temp.clear()
return encode
}
fn decode(data string) string {
mut decode :=""
mut temp := []u8{}
for value in data {
if value.is_digit() == false {
decode += value.repeat(temp.bytestr().int())
temp.clear()
}
else {temp << value}
}
return decode
}- Output:
12W1B12W3B24W1B14W WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Wren
import "./pattern" for Pattern
var p = Pattern.new("/u") // match any upper case letter
var encode = Fn.new { |s|
if (s == "") return s
var e = ""
var curr = s[0]
var count = 1
var i = 1
while (i < s.count) {
if (s[i] == curr) {
count = count + 1
} else {
e = e + count.toString + curr
curr = s[i]
count = 1
}
i = i + 1
}
return e + count.toString + curr
}
var decode = Fn.new { |e|
if (e == "") return e
var letters = Pattern.matchesText(p.findAll(e))
var numbers = p.splitAll(e)[0..-2].map { |s| Num.fromString(s) }.toList
return (0...letters.count).reduce("") { |acc, i| acc + letters[i]*numbers[i] }.join()
}
var strings = [
"AA",
"RROSETTAA",
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
]
for (s in strings) {
System.print("Original text : %(s)")
var e = encode.call(s)
System.print("Encoded text : %(e)")
var d = decode.call(e)
System.print("Decoded text : %(d)")
System.print("Original = decoded : %(s == d)\n")
}- Output:
Original text : AA Encoded text : 2A Decoded text : AA Original = decoded : true Original text : RROSETTAA Encoded text : 2R1O1S1E2T2A Decoded text : RROSETTAA Original = decoded : true Original text : WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Encoded text : 12W1B12W3B24W1B14W Decoded text : WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW Original = decoded : true
XPL0
include c:\cxpl\codes; \intrinsic 'code' declarations
string 0; \use zero-terminated strings, instead of MSb terminated
proc Compress(S); \Compress string using run-length encoding, & display it
char S;
int I, C0, C, N;
[I:= 0;
C0:= S(I); I:= I+1;
repeat ChOut(0, C0);
N:= 0;
repeat C:= S(I); I:= I+1;
N:= N+1;
until C#C0;
if N>1 then IntOut(0, N-1);
C0:= C;
until C=0;
]; \Compress
proc Expand(S); \Expand compressed string, and display it
char S;
int I, C0, C, N;
[I:= 0;
C0:= S(I); I:= I+1;
repeat ChOut(0, C0);
C:= S(I); I:= I+1;
if C>=^1 & C<=^9 then
[N:= 0;
while C>=^0 & C<=^9 do
[N:= N*10 + C-^0;
C:= S(I); I:= I+1;
];
while N do [ChOut(0, C0); N:= N-1];
];
C0:= C;
until C=0;
]; \Expand
[Compress("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW");
CrLf(0);
Expand("W11BW11B2W23BW13"); CrLf(0);
]Output (with slightly better compression than the example):
W11BW11B2W23BW13 WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Zig
const std = @import("std");
fn Run(comptime T: type) type {
return struct {
value: T,
length: usize,
};
}
fn encode(
comptime T: type,
input: []const T,
allocator: std.mem.Allocator,
) ![]Run(T) {
var runs = std.ArrayList(Run(T)).init(allocator);
defer runs.deinit();
var previous: ?T = null;
var length: usize = 0;
for (input) |current| {
if (previous == current) {
length += 1;
} else if (previous) |value| {
try runs.append(.{
.value = value,
.length = length,
});
previous = current;
length = 1;
} else {
previous = current;
length += 1;
}
}
if (previous) |value| {
try runs.append(.{
.value = value,
.length = length,
});
}
return runs.toOwnedSlice();
}
test encode {
const input =
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
const expected = [_]Run(u8){
.{ .length = 12, .value = 'W' },
.{ .length = 1, .value = 'B' },
.{ .length = 12, .value = 'W' },
.{ .length = 3, .value = 'B' },
.{ .length = 24, .value = 'W' },
.{ .length = 1, .value = 'B' },
.{ .length = 14, .value = 'W' },
};
const allocator = std.testing.allocator;
const actual = try encode(u8, input, allocator);
defer allocator.free(actual);
try std.testing.expectEqual(expected.len, actual.len);
for (expected, actual) |e, a| {
try std.testing.expectEqual(e.length, a.length);
try std.testing.expectEqual(e.value, a.value);
}
}
fn decode(
comptime T: type,
runs: []const Run(T),
allocator: std.mem.Allocator,
) ![]T {
var values = std.ArrayList(T).init(allocator);
defer values.deinit();
for (runs) |r|
try values.appendNTimes(r.value, r.length);
return values.toOwnedSlice();
}
test decode {
const runs = [_]Run(u8){
.{ .length = 12, .value = 'W' },
.{ .length = 1, .value = 'B' },
.{ .length = 12, .value = 'W' },
.{ .length = 3, .value = 'B' },
.{ .length = 24, .value = 'W' },
.{ .length = 1, .value = 'B' },
.{ .length = 14, .value = 'W' },
};
const allocator = std.testing.allocator;
const decoded = try decode(u8, &runs, allocator);
defer allocator.free(decoded);
try std.testing.expectEqualStrings(
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
decoded,
);
}
pub fn main() !void {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
defer std.debug.assert(gpa.deinit() == .ok);
const allocator = gpa.allocator();
var input = std.ArrayList(u8).init(allocator);
defer input.deinit();
const stdout = std.io.getStdOut().writer();
const stdin = std.io.getStdIn().reader();
try stdout.print("Input: ", .{});
try stdin.streamUntilDelimiter(input.writer(), '\n', null);
const runs = try encode(u8, input.items, allocator);
defer allocator.free(runs);
try stdout.print("Encoded:\n", .{});
for (runs) |r|
try stdout.print(" {}\n", .{r});
const decoded = try decode(u8, runs, allocator);
defer allocator.free(decoded);
try stdout.print("Decoded: {s}\n", .{decoded});
}- Output:
Input: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
Encoded:
run_length_encoding.Run(u8){ .value = 87, .length = 12 }
run_length_encoding.Run(u8){ .value = 66, .length = 1 }
run_length_encoding.Run(u8){ .value = 87, .length = 12 }
run_length_encoding.Run(u8){ .value = 66, .length = 3 }
run_length_encoding.Run(u8){ .value = 87, .length = 24 }
run_length_encoding.Run(u8){ .value = 66, .length = 1 }
run_length_encoding.Run(u8){ .value = 87, .length = 14 }
Decoded: WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW
zkl
A byte stream to byte stream codec, the streams hard coded for ease. Character '\1' is used as a sentinel and there are limits on the run length to avoid byte overflow.
const MAX_LEN=250, MIN_LEN=3;
fcn compress(text){ // !empty byte/text stream -->Data (byte stream)
sink:=Data(); cnt:=Ref(0);
write:='wrap(c,n){ // helper function
while(n>MAX_LEN){
sink.write(1); sink.write(MAX_LEN); sink.write(c);
n-=MAX_LEN;
}
if(n>MIN_LEN){ sink.write(1); sink.write(n); sink.write(c); }
else { do(n) { sink.write(c); } }
};
text.reduce('wrap(a,b){
if(a==b) cnt.inc();
else{ write(a,cnt.value); cnt.set(1); }
b
},text[0]) : write(_,cnt.value);
sink;
}fcn inflate(data){ //-->String
data.howza(3).pump(String,
fcn(c){ // if c==1, read n,c2 and expand, else write c
if(c=="\x01") return(Void.Read,2) else return(Void.Write,c) },
fcn(_,n,c){ c*n.toAsc() })
}text:="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
d:=compress(text);
d.bytes().println();
println(text.len()," bytes --> ",d.len()," bytes");
println(text==inflate(d));- Output:
L(1,12,87,66,1,12,87,66,66,66,1,24,87,66,1,14,87) 67 bytes --> 17 bytes True
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