2016 Update

Task/Caesar-cipher/Lua/caesar-cipher-2.lua

@@ -0,0 +1,32 @@
+local memo = {}
+
+local function make_table(k)
+    local t = {}
+    local a, A = ('a'):byte(), ('A'):byte()
+
+    for i = 0,25 do
+        local  c = a + i
+        local  C = A + i
+        local rc = a + (i+k) % 26
+        local RC = A + (i+k) % 26
+        t[c], t[C] = rc, RC
+    end
+
+    return t
+end
+
+local function caesar(str, k, decode)
+    k = (decode and -k or k) % 26
+
+    local t = memo[k]
+    if not t then
+        t = make_table(k)
+        memo[k] = t
+    end
+
+    local res_t = { str:byte(1,-1) }
+    for i,c in ipairs(res_t) do
+        res_t[i] = t[c] or c
+    end
+    return string.char(unpack(res_t))
+end