Rosetta Code

LZW compression: Difference between revisions

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Updated to work with Nim 1.4: removed test to "nil". Several other minor changes.
Line 3,540:
 
=={{header|Nim}}==
<lang>import tables
import tables
 
proc compress*(uncompressed: string): seq[int] =
## build the dictionary▼
var dictionary = initTable[string, int]()▼
for i in 0..255:▼
dictionary.add($char(i), i)
 
▲ ## buildBuild the dictionary.
var w: string = newString(0)
var compresseddictionary: = newSeqTable[string, int]()
▲ for i in 0..255: dictionary[$chr(i)] = i
 
var w = ""
for c in uncompressed:
var wc = w & c
if(dictionary.hasKey( wc)) in dictionary:
w = wc
else:
# writesWrites "w" to output.
compressedresult.add( dictionary[w])
# "wc" is a new sequence;: add it to the dictionary.
dictionary.add([wc,] = dictionary.len)
w = $c
 
# writeWrite remaining output if necessary.
if w.len compressed> 0: result.add( dictionary[w])▼
if(w != nil):
▲ compressed.add(dictionary[w])
 
result = compressed▼
 
proc decompress*(compressed: var seq[int]): string =
# build the dictionary▼
var dictionary = initTable[int, string]()
for i in 0..255:▼
dictionary.add(i, $char(i))
 
var# w:Build string =the dictionary[compressed[0]].
▲ var dictionary: = initTableTable[stringint, intstring]()
▲ for i in 0..255: dictionary[i] = $chr(i)
 
▲ resultvar w = dictionary[compressed[0]]
compressed.delete(0)
 
var decompressedresult = w
 
for k in compressed:
var entry: string = newString(0)
▲ # build theif k in dictionary:
if(dictionary.hasKey(k)):
entry = dictionary[k]
elif( k == dictionary.len):
entry = w & w[0]
else:
raise newException(ValueError, "Bad compressed k: " & $k)
result.add entry
 
# newNew sequence;: add it to the dictionary.▼
decompressed &= entry
dictionary.add([dictionary.len,] = w & entry[0])▼
 
▲ # new sequence; add it to the dictionary
▲ dictionary.add(dictionary.len, w & entry[0])
 
w = entry
 
result = decompressed
 
when isMainModule:
Line 3,603 ⟶ 3,592:
echo compressed
var decompressed = decompress(compressed)
echo decompressed</lang>
 
</lang>
{{Outout}}
<pre>@[84, 79, 66, 69, 79, 82, 78, 79, 84, 256, 258, 260, 265, 259, 261, 263]▼
<pre>
TOBEORNOTTOBEORTOBEORNOT</pre>▼
▲@[84, 79, 66, 69, 79, 82, 78, 79, 84, 256, 258, 260, 265, 259, 261, 263]
▲TOBEORNOTTOBEORTOBEORNOT
</pre>
 
=={{header|Objeck}}==
Retrieved from "https://rosettacode.org/wiki/LZW_compression"