Data update

Task/Burrows-Wheeler-transform/Pluto/burrows-wheeler-transform.pluto

@@ -0,0 +1,59 @@
+require "table2"
+
+$define STX = "\x02"
+$define ETX = "\x03"
+
+local function bwt(s)
+    if s:find(STX, 1, true) or s:find(ETX, 1, true) then return nil end
+    s = STX .. s .. ETX
+    local len = #s
+    local tbl = table.rep(len, "")
+    tbl[1] = s
+    for i = 2, len do tbl[i] = s:sub(i) .. s:sub(1, i - 1) end
+    tbl:sort()
+    local last_chars = table.rep(len, "")
+    for i = 1, len do last_chars[i] = tbl[i][len] end
+    return last_chars:concat()
+end
+
+local function ibwt(r)
+    local len = #r
+    if len == 0 then return "" end
+    local tbl = table.rep(len, "")
+    for i = 1, len do
+        for j = 1, len do tbl[j] = r[j].. tbl[j] end
+        tbl:sort()
+    end
+    for tbl as row do
+        if row:endswith(ETX) then return row:sub(2, -2) end
+    end
+    return ""
+end
+
+local function make_printable(s)
+    -- Substitute ^ for STX and | for ETX to print results.
+    s = s:replace(STX, "^")
+    return s:replace(ETX, "|")
+end
+
+local tests = {
+    "banana",
+    "appellee",
+    "dogwood",
+    "TO BE OR NOT TO BE OR WANT TO BE OR NOT?",
+    "SIX.MIXED.PIXIES.SIFT.SIXTY.PIXIE.DUST.BOXES",
+    "\x02ABC\x03"
+}
+for tests as test do
+    print(make_printable(test))
+    io.write(" --> ")
+    local t = bwt(test)
+    if !t then
+        print("ERROR: String can't contain STX or ETX")
+        t = ""
+    else
+        print(make_printable(t))
+    end
+    local r = ibwt(t)
+    print($" --> {r}\n")
+end