Data commit

Task/LZW-compression/C-sharp/lzw-compression.cs

@@ -0,0 +1,81 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LZW
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            List<int> compressed = Compress("TOBEORNOTTOBEORTOBEORNOT");
+            Console.WriteLine(string.Join(", ", compressed));
+            string decompressed = Decompress(compressed);
+            Console.WriteLine(decompressed);
+        }
+
+        public static List<int> Compress(string uncompressed)
+        {
+            // build the dictionary
+            Dictionary<string, int> dictionary = new Dictionary<string, int>();
+            for (int i = 0; i < 256; i++)
+                dictionary.Add(((char)i).ToString(), i);
+
+            string w = string.Empty;
+            List<int> compressed = new List<int>();
+
+            foreach (char c in uncompressed)
+            {
+                string wc = w + c;
+                if (dictionary.ContainsKey(wc))
+                {
+                    w = wc;
+                }
+                else
+                {
+                    // write w to output
+                    compressed.Add(dictionary[w]);
+                    // wc is a new sequence; add it to the dictionary
+                    dictionary.Add(wc, dictionary.Count);
+                    w = c.ToString();
+                }
+            }
+
+            // write remaining output if necessary
+            if (!string.IsNullOrEmpty(w))
+                compressed.Add(dictionary[w]);
+
+            return compressed;
+        }
+
+        public static string Decompress(List<int> compressed)
+        {
+            // build the dictionary
+            Dictionary<int, string> dictionary = new Dictionary<int, string>();
+            for (int i = 0; i < 256; i++)
+                dictionary.Add(i, ((char)i).ToString());
+
+            string w = dictionary[compressed[0]];
+            compressed.RemoveAt(0);
+            StringBuilder decompressed = new StringBuilder(w);
+
+            foreach (int k in compressed)
+            {
+                string entry = null;
+                if (dictionary.ContainsKey(k))
+                    entry = dictionary[k];
+                else if (k == dictionary.Count)
+                    entry = w + w[0];
+
+                decompressed.Append(entry);
+
+                // new sequence; add it to the dictionary
+                dictionary.Add(dictionary.Count, w + entry[0]);
+
+                w = entry;
+            }
+
+            return decompressed.ToString();
+        }
+    }
+}