Initial data commit

Task/LZW-compression/JavaScript/lzw-compression-1.js

@@ -0,0 +1,81 @@
+//LZW Compression/Decompression for Strings
+var LZW = {
+    compress: function (uncompressed) {
+        "use strict";
+        // Build the dictionary.
+        var i,
+            dictionary = {},
+            c,
+            wc,
+            w = "",
+            result = [],
+            dictSize = 256;
+        for (i = 0; i < 256; i += 1) {
+            dictionary[String.fromCharCode(i)] = i;
+        }
+
+        for (i = 0; i < uncompressed.length; i += 1) {
+            c = uncompressed.charAt(i);
+            wc = w + c;
+            //Do not use dictionary[wc] because javascript arrays
+            //will return values for array['pop'], array['push'] etc
+           // if (dictionary[wc]) {
+            if (dictionary.hasOwnProperty(wc)) {
+                w = wc;
+            } else {
+                result.push(dictionary[w]);
+                // Add wc to the dictionary.
+                dictionary[wc] = dictSize++;
+                w = String(c);
+            }
+        }
+
+        // Output the code for w.
+        if (w !== "") {
+            result.push(dictionary[w]);
+        }
+        return result;
+    },
+
+
+    decompress: function (compressed) {
+        "use strict";
+        // Build the dictionary.
+        var i,
+            dictionary = [],
+            w,
+            result,
+            k,
+            entry = "",
+            dictSize = 256;
+        for (i = 0; i < 256; i += 1) {
+            dictionary[i] = String.fromCharCode(i);
+        }
+
+        w = String.fromCharCode(compressed[0]);
+        result = w;
+        for (i = 1; i < compressed.length; i += 1) {
+            k = compressed[i];
+            if (dictionary[k]) {
+                entry = dictionary[k];
+            } else {
+                if (k === dictSize) {
+                    entry = w + w.charAt(0);
+                } else {
+                    return null;
+                }
+            }
+
+            result += entry;
+
+            // Add w+entry[0] to the dictionary.
+            dictionary[dictSize++] = w + entry.charAt(0);
+
+            w = entry;
+        }
+        return result;
+    }
+}, // For Test Purposes
+    comp = LZW.compress("TOBEORNOTTOBEORTOBEORNOT"),
+    decomp = LZW.decompress(comp);
+document.write(comp + '<br>' + decomp);

Task/LZW-compression/JavaScript/lzw-compression-2.js

@@ -0,0 +1,110 @@
+'use strict';
+/**
+    Namespace for LZW compression and decompression.
+    Methods:
+        LZW.compress(uncompressed)
+        LZW.decompress(compressed)
+*/
+class LZW
+{
+    /**
+        Perform the LZW compression
+        uncompressed - String. The string on which to perform the compression.
+    */
+    static compress(uncompressed)
+    {
+        // Initialize dictionary
+        let dictionary = {};
+        for (let i = 0; i < 256; i++)
+        {
+            dictionary[String.fromCharCode(i)] = i;
+        }
+
+        let word = '';
+        let result = [];
+        let dictSize = 256;
+
+        for (let i = 0, len = uncompressed.length; i < len; i++)
+        {
+            let curChar = uncompressed[i];
+            let joinedWord = word + curChar;
+
+            // Do not use dictionary[joinedWord] because javascript objects
+            // will return values for myObject['toString']
+            if (dictionary.hasOwnProperty(joinedWord))
+            {
+                word = joinedWord;
+            }
+            else
+            {
+                result.push(dictionary[word]);
+                // Add wc to the dictionary.
+                dictionary[joinedWord] = dictSize++;
+                word = curChar;
+            }
+        }
+
+        if (word !== '')
+        {
+            result.push(dictionary[word]);
+        }
+
+        return result;
+    }
+
+    /**
+        Decompress LZW array generated by LZW.compress()
+        compressed - Array. The array that holds LZW compressed data.
+    */
+    static decompress(compressed)
+    {
+        // Initialize Dictionary (inverse of compress)
+        let dictionary = {};
+        for (let i = 0; i < 256; i++)
+        {
+            dictionary[i] = String.fromCharCode(i);
+        }
+
+        let word = String.fromCharCode(compressed[0]);
+        let result = word;
+        let entry = '';
+        let dictSize = 256;
+
+        for (let i = 1, len = compressed.length; i < len; i++)
+        {
+            let curNumber = compressed[i];
+
+            if (dictionary[curNumber] !== undefined)
+            {
+                entry = dictionary[curNumber];
+            }
+            else
+            {
+                if (curNumber === dictSize)
+                {
+                    entry = word + word[0];
+                }
+                else
+                {
+                    throw 'Error in processing';
+                    return null;
+                }
+            }
+
+            result += entry;
+
+            // Add word + entry[0] to dictionary
+            dictionary[dictSize++] = word + entry[0];
+
+            word = entry;
+        }
+
+        return result;
+    }
+}
+
+let comp = LZW.compress('TOBEORNOTTOBEORTOBEORNOT');
+let decomp = LZW.decompress(comp);
+
+console.log(`${comp}
+${decomp}`);