diff --git a/day15/part1.lua b/day15/part1.lua
new file mode 100755
index 0000000..c743a56
--- /dev/null
+++ b/day15/part1.lua
@@ -0,0 +1,47 @@
+#!/usr/bin/env luajit
+require("utils")
+require("pqueue")
+
+local grid = {}
+for line in io.lines(arg[3]) do
+	local row = {}
+	for char in chars(line) do
+		table.insert(row, tonumber(char))
+	end
+	table.insert(grid, row)
+end
+
+function printgrid()
+	for r, row in pairs(grid) do
+		for c, cell in pairs(row) do
+			io.write(string.format("%3d", cell))
+		end
+		io.write('\n')
+	end
+end
+
+local pq = pqueue(function(a, b)
+	return a[3] < b[3]
+end)
+
+local distances = {}
+
+local H = math.huge
+local n = { 1, 1, 0 }
+while n ~= nil and (distances[#grid] == nil or distances[#grid][#grid[1]] == nil) do
+	local r, c, d = unpack(n)
+	if 0 < r or r <= #grid or 0 < c or c <= #grid[r] then
+		local row = distances[r] or {}
+		if d < (row[c] or H) then
+			row[c] = d
+			distances[r] = row
+			pq:add({ r-1, c, d + ((grid[r-1] or {})[c] or H) })
+			pq:add({ r, c-1, d + ((grid[r] or {})[c-1] or H) })
+			pq:add({ r+1, c, d + ((grid[r+1] or {})[c] or H) })
+			pq:add({ r, c+1, d + ((grid[r] or {})[c+1] or H) })
+		end
+	end
+	n = pq:pop()
+end
+
+print(distances[#grid] and distances[#grid][#grid[1]])
diff --git a/day15/part2.lua b/day15/part2.lua
new file mode 100755
index 0000000..ccec019
--- /dev/null
+++ b/day15/part2.lua
@@ -0,0 +1,60 @@
+#!/usr/bin/env luajit
+require("utils")
+require("pqueue")
+
+local grid = {}
+for line in io.lines(arg[3]) do
+	local row = {}
+	for char in chars(line) do
+		table.insert(row, tonumber(char))
+	end
+	table.insert(grid, row)
+end
+
+function printgrid()
+	for r, row in pairs(grid) do
+		for c, cell in pairs(row) do
+			io.write(string.format("%3d", cell))
+		end
+		io.write('\n')
+	end
+end
+
+local h, w = #grid, #grid[1]
+for r0 = 0, 4 do
+	for c0 = 0, 4 do
+		for r = 1, h do
+			for c = 1, w do
+				local row = grid[r0*h + r] or {}
+				row[c0*w + c] = (grid[r][c] + r0 + c0 - 1) % 9 + 1
+				grid[r0*h + r] = row
+			end
+		end
+	end
+end
+
+local pq = pqueue(function(a, b)
+	return a[3] < b[3]
+end)
+
+local distances = {}
+
+local H = math.huge
+local n = { 1, 1, 0 }
+while n ~= nil and (distances[#grid] == nil or distances[#grid][#grid[1]] == nil) do
+	local r, c, d = unpack(n)
+	if 0 < r or r <= #grid or 0 < c or c <= #grid[r] then
+		local row = distances[r] or {}
+		if d < (row[c] or H) then
+			row[c] = d
+			distances[r] = row
+			pq:add({ r-1, c, d + ((grid[r-1] or {})[c] or H) })
+			pq:add({ r, c-1, d + ((grid[r] or {})[c-1] or H) })
+			pq:add({ r+1, c, d + ((grid[r+1] or {})[c] or H) })
+			pq:add({ r, c+1, d + ((grid[r] or {})[c+1] or H) })
+		end
+	end
+	n = pq:pop()
+end
+
+print(distances[#grid] and distances[#grid][#grid[1]])
diff --git a/pqueue.lua b/pqueue.lua
new file mode 100644
index 0000000..674a7eb
--- /dev/null
+++ b/pqueue.lua
@@ -0,0 +1,49 @@
+local function add(self, item)
+	table.insert(self.items, item)
+	local i, p = #self.items
+	local p = math.floor(i / 2)
+	while i > 1 and self.smaller(self.items[i], self.items[p]) do
+		self.items[p], self.items[i] = self.items[i], self.items[p]
+		i, p = p, math.floor(p / 2)
+	end
+end
+
+local function pop(self)
+	local item = self.items[1]
+	self.items[1] = self.items[#self.items]
+	table.remove(self.items)
+	local i = 1
+	while i * 2 <= #self.items do
+		if i * 2 + 1 <= #self.items then
+			if self.smaller(self.items[i*2], self.items[i])
+			or self.smaller(self.items[i*2+1], self.items[i]) then
+				if self.smaller(self.items[i*2], self.items[i*2+1]) then
+					self.items[i], self.items[i*2], i
+						= self.items[i * 2], self.items[i], i * 2
+				else
+					self.items[i], self.items[i*2+1], i
+						= self.items[i*2+1], self.items[i], i * 2 + 1
+				end
+			else
+				break
+			end
+		else
+			if self.smaller(self.items[i*2], self.items[i]) then
+				self.items[i], self.items[i * 2]
+					= self.items[i * 2], self.items[i]
+			end
+			i = i * 2
+		end
+	end
+	return item
+end
+
+function pqueue(smaller)
+	return {
+		items = {},
+		smaller = smaller
+			or function(a, b) return a < b end,
+		add = add,
+		pop = pop,
+	}
+end
diff --git a/utils.lua b/utils.lua
index 1836650..9734e6f 100644
--- a/utils.lua
+++ b/utils.lua
@@ -24,11 +24,20 @@ function foreach(t, f)
 	end
 end
 
-function printtable(t)
+function printtable(t, nonewline)
 	for k, v in pairs(t) do
-		io.write(k..":"..v.." ")
+		io.write(k..":")
+		if type(v) == "table" then
+			io.write("(")
+			printtable(v, true)
+			io.write(") ")
+		else
+			io.write(v.." ")
+		end
+	end
+	if not nonewline then
+		io.write("\n")
 	end
-	io.write("\n")
 end
 
 function count(t, pred)