Added naive decode function

Yonaba · Yonaba · commit a29bff04ff4c · 2014-02-21T22:27:06.000Z
Prettified source
diff --git a/Burrows_Wheeler_Transform/Lua/Yonaba/bwt.lua b/Burrows_Wheeler_Transform/Lua/Yonaba/bwt.lua
@@ -1,24 +1,58 @@
 --Burrows-Wheeler Transform
 
-function encode(word)
-local t={word}
-local pos = 1
+--Burrows-Wheeler Transform
 
-local cat = string.len(word)
-	for i=cat-1,1,-1 do
-	local tmp = string.sub(word,1,i)
-	local comp = string.sub(word,i+1,cat)
-	local str = comp..tmp
 
-	table.insert(t,str)
-	end
-table.sort(t)
+function encode(word)
+  local t={word}
+  local pos = 1
+  local cat = string.len(word)
+  
+	for i=cat-1,1,-1 do
+    local tmp = string.sub(word,1,i)
+    local comp = string.sub(word,i+1,cat)
+    local str = comp..tmp
+    table.insert(t,str)
+  end
+  
+  table.sort(t)
 
-local retStr = ""
+  local retStr = ""
 	for k in ipairs(t) do
 		if t[k]==word then pos = k end
 		retStr = retStr..string.sub(t[k],string.len(t[k]),string.len(t[k]))
 	end
 
-return retStr
+  return retStr
 end
+
+
+function decode(encword)
+  --print('decode',encword)
+  local size = string.len(encword)
+  local offset = tonumber(string.sub(encword,1,1))
+  local encword = string.sub(encword,2,size)
+
+  local t={}
+	for n=0,string.len(encword),1 do
+		for i=1,string.len(encword),1 do
+      t[i] = not t[i] and '' or string.sub(encword,i,i)..t[i]
+		end
+		table.sort(t)
+	end
+	
+  return (t[offset])
+end
+
+--Sample Test
+local str = "SIX.MIXED.PIXIES.SIFT.SIXTY.PIXIE.DUST.BOXES"
+local out = ''
+	--for w in string.gfind(str, "%w+") do
+	local enc = encode(str)
+	local dec = decode(enc)
+	out = out .. '.'..enc
+	print("\nChaine originale: "..str)
+	print("Transformée B-W: "..enc)
+	print("Transformée Décodée: "..dec)
+	--end
+print(out)
