A-M baby

Task/LZW-compression/Go/lzw-compression.go

@@ -0,0 +1,72 @@
+package main
+import "fmt"
+
+// Compress a string to a list of output symbols.
+func compress(uncompressed string) []int {
+    // Build the dictionary.
+    dictSize := 256
+    dictionary := make(map[string]int)
+    for i := 0; i < 256; i++ {
+        dictionary[string(i)] = i
+    }
+
+    w := ""
+    result := make([]int, 0)
+    for _, c := range []byte(uncompressed) {
+        wc := w + string(c)
+        if _, ok := dictionary[wc]; ok {
+            w = wc
+        } else {
+            result = append(result, dictionary[w])
+            // Add wc to the dictionary.
+            dictionary[wc] = dictSize
+            dictSize++
+            w = string(c)
+        }
+    }
+
+    // Output the code for w.
+    if w != "" {
+        result = append(result, dictionary[w])
+    }
+    return result
+}
+
+// Decompress a list of output ks to a string.
+func decompress(compressed []int) string {
+    // Build the dictionary.
+    dictSize := 256
+    dictionary := make(map[int]string)
+    for i := 0; i < 256; i++ {
+        dictionary[i] = string(i)
+    }
+
+    w := string(compressed[0])
+    result := w
+    for _, k := range compressed[1:] {
+        var entry string
+        if x, ok := dictionary[k]; ok {
+            entry = x
+        } else if k == dictSize {
+            entry = w + w[:1]
+        } else {
+            panic(fmt.Sprintf("Bad compressed k: %d", k))
+        }
+
+        result += entry
+
+        // Add w+entry[0] to the dictionary.
+        dictionary[dictSize] = w + entry[:1]
+        dictSize++
+
+        w = entry
+    }
+    return result
+}
+
+func main() {
+    compressed := compress("TOBEORNOTTOBEORTOBEORNOT")
+    fmt.Println(compressed)
+    decompressed := decompress(compressed)
+    fmt.Println(decompressed)
+}