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Commit25dc6aa

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LZW Encoding/Decoding
Lempel–Ziv–Welch (LZW) is a universal lossless data compressionalgorithm. It is an improved implementation of the LZ78 algorithm.
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‎src/compression/LZW/LZW.js

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/**
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* LZW Encoding/Decoding
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*
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* Lempel–Ziv–Welch (LZW) is a universal lossless data
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* compression algorithm. It is an improved implementation
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* of the LZ78 algorithm.
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*
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*@example
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* var lzwModule = require('path-to-algorithms/src/compression'+
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* '/LZW/LZW');
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* var lzw = new lzwModule.LZW();
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*
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* var compressed = lzw.compress("ABCABCABCABCABCABC");
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* console.log(compressed);
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*
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* var decompressed = lzw.decompress(compressed);
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* console.log(decompressed);
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*
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*@module compression/LZW/LZW
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*/
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(function(exports){
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'use strict';
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exports.LZW=function(){
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this.dictionarySize=256;
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};
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exports.LZW.compress=function(data){
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vari;
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vardictionary={};
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varcharacter;
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varwc;
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varw='';
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varresult=[];
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for(i=0;i<this.dictionarySize;i=i+1){
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dictionary[String.fromCharCode(i)]=i;
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}
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for(i=0;i<data.length;i=i+1){
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character=data.charAt(i);
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wc=w+character;
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if(dictionary.hasOwnProperty(wc)){
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w=wc;
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}else{
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result.push(dictionary[w]);
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dictionary[wc]=this.dictionarySize;
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this.dictionarySize=this.dictionarySize+1;
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w=String(character);
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}
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}
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if(w!==''){
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result.push(dictionary[w]);
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}
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returnresult;
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};
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exports.LZW.decompress=function(compressedData){
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vari;
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vardictionary=[];
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varw;
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varresult;
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varkey;
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varentry='';
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for(i=0;i<this.dictionarySize;i=i+1){
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dictionary[i]=String.fromCharCode(i);
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}
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w=String.fromCharCode(compressedData[0]);
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result=w;
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for(i=1;i<compressedData.length;i=i+1){
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key=compressedData[i];
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if(dictionary[key]){
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entry=dictionary[key];
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}else{
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if(key===this.dictionarySize){
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entry=w+w.charAt(0);
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}else{
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returnnull;
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}
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}
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result+=entry;
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dictionary[this.dictionarySize]=w+entry.charAt(0);
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this.dictionarySize=this.dictionarySize+1;
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w=entry;
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}
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returnresult;
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};
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})(typeofwindow==='undefined' ?module.exports :window);

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