Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs

Dashboard
Notifications
Mark all as read
Challenges

Run-length encode a byte sequence

+2
−0

Run-length encoding is a simple compression technique which compresses sequences of repeating identical bytes.

The encoding rules for this task are as follows:

Any sequence of $n$ identical bytes ($3 \leq n \leq 63$) is replaced by a byte with value n+0xc0 followed by only one copy of that byte. If any of the original bytes has value 0xc0 or above, such encoding also happens if that byte occurs only one or two times in a row (thus the encoded sequence may actually be longer if such bytes occur).

The task is to write a run-length encoder. The input is a sequence of bytes. It may be a sequence of actual bytes, or a sequence of numbers in the range 0 to 255 (inclusive), whichever is more convenient. The output is again a sequence of bytes (again, in any suitable form), which is the proper run-length encoding of the input sequence.

Examples (byte values are given in 2-digit hex):

00 01 02 03 04        → 00 01 02 03 04
00 00 00 01 01 00     → c3 00 01 01 00
be bf c0 c1 c2        → be bf c1 c0 c1 c1 c1 c2
00 00 00 … (63 bytes) → ff 00
00 00 00 … (64 bytes) → ff 00 00
00 00 00 … (65 bytes) → ff 00 00 00
00 00 00 … (66 bytes) → ff 00 c3 00
ff ff ff … (63 bytes) → ff ff
ff ff ff … (64 bytes) → ff ff c1 ff
ff ff ff … (65 bytes) → ff ff c2 ff
ff ff ff … (66 bytes) → ff ff c3 ff

This is a code-golf challenge; the shortest program for a language wins.

Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

0 comment threads

2 answers

+2
−0

JavaScript (Node.js), 101 82 bytes

-19 bytes thanks to Shaggy!

x=>x.replace(/(..)\1{0,62}/g,(c,g)=>c>'c'||c[5]?(192+c.length/2).toString(16)+g:c)

Try it online!

Everything can be solved with regexes.

Takes input and outputs as hex strings.

Why does this post require moderator attention?
You might want to add some details to your flag.

2 comment threads

82 bytes (1 comment)
Save 3 bytes (1 comment)
+2
−0

JavaScript (Node.js), 146 bytes

f=(a,c=n=~(b=d=[],e=x=>x&&(c>191|d>2?b.push(d+192,c):b.push(...d+n?[c,c]:[c]),c=n,d=0)))=>(a.map(b=>c^n?c=(e(d>62|b-c),d++,b):(c=b,d=1)),e(c-n),b)

Try it online!

Ungolfed version

Why does this post require moderator attention?
You might want to add some details to your flag.

0 comment threads

Sign up to answer this question »

This community is part of the Codidact network. We have other communities too — take a look!

You can also join us in chat!

Want to advertise this community? Use our templates!