June 2018 Update

Task/LZW-compression/Julia/lzw-compression.julia

@@ -0,0 +1,50 @@
+function compressLZW(decompressed::String)
+    dictsize = 256
+    dict     = Dict{String,Int}(string(Char(i)) => i for i in range(0, dictsize))
+    result   = Vector{Int}(0)
+    w        = ""
+    for c in decompressed
+        wc = string(w, c)
+        if haskey(dict, wc)
+            w = wc
+        else
+            push!(result, dict[w])
+            dict[wc]  = dictsize
+            dictsize += 1
+            w        = string(c)
+        end
+    end
+    if !isempty(w) push!(result, dict[w]) end
+    return result
+end
+
+function decompressLZW(compressed::Vector{Int})
+    dictsize = 256
+    dict     = Dict{Int,String}(i => string('\0' + i) for i in range(0, dictsize))
+    result   = IOBuffer()
+    w        = string(Char(shift!(compressed)))
+    write(result, w)
+    for k in compressed
+        if haskey(dict, k)
+            entry = dict[k]
+        elseif k == dictsize
+            entry = string(w, w[1])
+        else
+            error("bad compressed k: $k")
+        end
+        write(result, entry)
+        dict[dictsize] = string(w, entry[1])
+        dictsize += 1
+        w = entry
+    end
+    return String(result)
+end
+
+original     = ["0123456789", "TOBEORNOTTOBEORTOBEORNOT", "dudidudidudida"]
+compressed   = compressLZW.(original)
+decompressed = decompressLZW.(compressed)
+
+for (word, comp, decomp) in zip(original, compressed, decompressed)
+    comprate = (length(word) - length(comp)) / length(word) * 100
+    println("Original: $word\n-> Compressed: $comp (compr.rate: $(round(comprate, 2))%)\n-> Decompressed: $decomp")
+end