Data commit

Task/Move-to-front-algorithm/Lua/move-to-front-algorithm.lua

@@ -0,0 +1,46 @@
+-- Return table of the alphabet in lower case
+function getAlphabet ()
+    local letters = {}
+    for ascii = 97, 122 do table.insert(letters, string.char(ascii)) end
+    return letters
+end
+
+-- Move the table value at ind to the front of tab
+function moveToFront (tab, ind)
+    local toMove = tab[ind]
+    for i = ind - 1, 1, -1 do tab[i + 1] = tab[i] end
+    tab[1] = toMove
+end
+
+-- Perform move-to-front encoding on input
+function encode (input)
+    local symbolTable, output, index = getAlphabet(), {}
+    for pos = 1, #input do
+        for k, v in pairs(symbolTable) do
+            if v == input:sub(pos, pos) then index = k end
+        end
+        moveToFront(symbolTable, index)
+        table.insert(output, index - 1)
+    end
+    return table.concat(output, " ")
+end
+
+-- Perform move-to-front decoding on input
+function decode (input)
+    local symbolTable, output = getAlphabet(), ""
+    for num in input:gmatch("%d+") do
+        output = output .. symbolTable[num + 1]
+        moveToFront(symbolTable, num + 1)
+    end
+    return output
+end
+
+-- Main procedure
+local testCases, output = {"broood", "bananaaa", "hiphophiphop"}
+for _, case in pairs(testCases) do
+    output = encode(case)
+    print("Original string: " .. case)
+    print("Encoded: " .. output)
+    print("Decoded: " .. decode(output))
+    print()
+end