diff --git a/day23/part1.lua b/day23/part1.lua
new file mode 100755
index 0000000..b64b055
--- /dev/null
+++ b/day23/part1.lua
@@ -0,0 +1,153 @@
+#!/usr/bin/env luajit
+require("utils")
+
+local targets = { A=3, B=5, C=7, D=9 }
+local costs = { A=1, B=10, C=100, D=1000 }
+
+local f = io.open(arg[3])
+local line = f:read("*l") -- #####
+line = f:read("*l") -- #...#
+local hall = {}
+local length = #line - 2
+line = f:read("*l") -- ##A#B##
+local rooms = {}
+local depth = 1
+local ncorrect = 0
+while line do
+	local l = 0
+	for char in chars(line) do
+		if char ~= "#" and char ~= " " then
+			if rooms[l] == nil then rooms[l] = {} end
+			table.insert(rooms[l], char)
+			if targets[char] == l then ncorrect = ncorrect + 1 end
+		end
+		l = l + 1
+	end
+	line = f:read("*l") -- ##A#B##
+	depth = depth + 1
+end
+depth = depth - 2
+
+function printit()
+	for l = 1, length do io.write(hall[l] or ".") end
+	io.write("\n")
+	for d = 1, depth do
+		for l = 1, length do
+			if rooms[l] then
+				io.write(rooms[l][d] or ".")
+			else
+				io.write(" ")
+			end
+		end
+		io.write("\n")
+	end
+end
+
+printit()
+
+function addtoroom(rooms, room, char)
+	local room = rooms[room]
+	for d = depth, 1, -1 do
+		if room[d] == nil then
+			room[d] = char
+			return
+		end
+	end
+end
+
+function removefromroom(rooms, i)
+	local room = rooms[i]
+	if room[1] == nil then
+		if room[2] == nil then
+			return
+		else
+			local c = room[2]
+			room[2] = nil
+			return c, 2, targets[c] == i
+		end
+	else
+		local c = room[1]
+		room[1] = nil
+		return c, 1, targets[c] == i and targets[room[2]] == i
+	end
+end
+
+function pathtoroom(l, c, hall, rooms)
+	local t = targets[c]
+	if rooms[t][1] ~= nil then return end
+	for p = l + sign(t - l), t, sign(t - l) do
+		if hall[p] ~= nil then return end
+	end
+	local room = rooms[t]
+	if room[2] == nil and room[1] == nil then
+		return t, math.abs(t - l) + 2
+	elseif room[2] == c and room[1] == nil then
+		return t, math.abs(t - l) + 1
+	end
+end
+
+local nhall = 0
+local minscore = math.huge
+-- global: length, depth, hall, rooms, ncorrect, nhall, minscore
+-- returns: score
+function backtrack(step, score)
+	-- print(step)
+	-- printit()
+	if step > 16 then
+	elseif ncorrect == 8 and score < minscore then
+		minscore = score
+		print(minscore)
+	elseif score > minscore then
+	else
+		-- move into rooms
+		for l = 1, length do
+			if hall[l] ~= nil then
+				local c = hall[l]
+				local room, distance = pathtoroom(l, c, hall, rooms)
+				if room then
+					hall[l] = nil
+					addtoroom(rooms, room, c)
+					ncorrect = ncorrect + 1
+					backtrack(step + 1, score + distance * costs[c])
+					ncorrect = ncorrect - 1
+					removefromroom(rooms, room)
+					hall[l] = c
+				end
+			end
+		end
+		-- remove from rooms
+		for l, room in pairs(rooms) do
+			local c, distance, complete = removefromroom(rooms, l)
+			if c ~= nil then
+				if not complete then
+					if targets[c] == l then ncorrect = ncorrect - 1 end
+					-- left
+					local t = l - 1
+					while t >= 1 and hall[t] == nil do
+						if rooms[t] == nil then
+							hall[t] = c
+							backtrack(step + 1, score + (distance + l - t) * costs[c])
+							hall[t] = nil
+						end
+						t = t - 1
+					end
+					-- right
+					local t = l + 1
+					while t <= length and hall[t] == nil do
+						if rooms[t] == nil then
+							hall[t] = c
+							backtrack(step + 1, score + (distance + t - l) * costs[c])
+							hall[t] = nil
+						end
+						t = t + 1
+					end
+					if targets[c] == l then ncorrect = ncorrect + 1 end
+				end
+				addtoroom(rooms, l, c)
+			end
+		end
+	end
+end
+
+backtrack(0, 0)
+print(minscore)
diff --git a/day23/part2.lua b/day23/part2.lua
new file mode 100755
index 0000000..cef4253
--- /dev/null
+++ b/day23/part2.lua
@@ -0,0 +1,157 @@
+#!/usr/bin/env luajit
+require("utils")
+
+local targets = { A=3, B=5, C=7, D=9 }
+local costs = { A=1, B=10, C=100, D=1000 }
+
+local f = io.open(arg[3])
+local line = f:read("*l") -- #####
+line = f:read("*l") -- #...#
+local hall = {}
+local length = #line - 2
+line = f:read("*l") -- ##A#B##
+local rooms = {}
+local depth = 1
+local ncorrect = 0
+while line do
+	local l = 0
+	for char in chars(line) do
+		if char ~= "#" and char ~= " " then
+			if rooms[l] == nil then rooms[l] = {} end
+			table.insert(rooms[l], char)
+			if targets[char] == l then ncorrect = ncorrect + 1 end
+		end
+		l = l + 1
+	end
+	line = f:read("*l") -- ##A#B##
+	depth = depth + 1
+end
+
+table.insert(rooms[3], 2, "D")
+table.insert(rooms[3], 2, "D")
+table.insert(rooms[5], 2, "B"); ncorrect = ncorrect + 1 -- this line
+table.insert(rooms[5], 2, "C")
+table.insert(rooms[7], 2, "A")
+table.insert(rooms[7], 2, "B")
+table.insert(rooms[9], 2, "C")
+table.insert(rooms[9], 2, "A")
+
+function printit()
+	for l = 1, length do io.write(hall[l] or ".") end
+	io.write("\n")
+	for d = 1, depth do
+		for l = 1, length do
+			if rooms[l] then
+				io.write(rooms[l][d] or ".")
+			else
+				io.write(" ")
+			end
+		end
+		io.write("\n")
+	end
+end
+
+printit()
+
+function addtoroom(rooms, room, char)
+	local room = rooms[room]
+	for d = depth, 1, -1 do
+		if room[d] == nil then
+			room[d] = char
+			return
+		end
+	end
+end
+
+function removefromroom(rooms, i)
+	local room = rooms[i]
+	local c, dst, complete = nil, nil, true
+	for d = depth, 1, -1 do
+		if room[d] ~= nil then
+			c, dst = room[d], d
+			if targets[c] ~= i then complete = false end
+		end
+	end
+	if dst then room[dst] = nil end
+	return c, dst, complete
+end
+
+function pathtoroom(l, c, hall, rooms)
+	local t = targets[c]
+	if rooms[t][1] ~= nil then return end
+	for p = l + sign(t - l), t, sign(t - l) do
+		if hall[p] ~= nil then return end
+	end
+	local room = rooms[t]
+	for d = depth, 1, -1 do
+		if room[d] == nil then
+			return t, math.abs(t - l) + d
+		elseif room[d] ~= c then
+			return
+		end
+	end
+end
+
+local nhall = 0
+local minscore = math.huge
+-- global: length, depth, hall, rooms, ncorrect, nhall, minscore
+-- returns: score
+function backtrack(step, score)
+	if step > 32 then
+	elseif ncorrect == 16 and score < minscore then
+		minscore = score
+		print(minscore)
+	elseif score > minscore then
+	else
+		-- move into rooms
+		for l = 1, length do
+			if hall[l] ~= nil then
+				local c = hall[l]
+				local room, distance = pathtoroom(l, c, hall, rooms)
+				if room then
+					hall[l] = nil
+					addtoroom(rooms, room, c)
+					ncorrect = ncorrect + 1
+					backtrack(step + 1, score + distance * costs[c])
+					ncorrect = ncorrect - 1
+					removefromroom(rooms, room)
+					hall[l] = c
+				end
+			end
+		end
+		-- remove from rooms
+		for l, room in pairs(rooms) do
+			local c, distance, complete = removefromroom(rooms, l)
+			if c ~= nil then
+				if not complete then
+					if targets[c] == l then ncorrect = ncorrect - 1 end
+					-- left
+					local t = l - 1
+					while t >= 1 and hall[t] == nil do
+						if rooms[t] == nil then
+							hall[t] = c
+							backtrack(step + 1, score + (distance + l - t) * costs[c])
+							hall[t] = nil
+						end
+						t = t - 1
+					end
+					-- right
+					local t = l + 1
+					while t <= length and hall[t] == nil do
+						if rooms[t] == nil then
+							hall[t] = c
+							backtrack(step + 1, score + (distance + t - l) * costs[c])
+							hall[t] = nil
+						end
+						t = t + 1
+					end
+					if targets[c] == l then ncorrect = ncorrect + 1 end
+				end
+				addtoroom(rooms, l, c)
+			end
+		end
+	end
+end
+
+backtrack(0, 0)
+print(minscore)