day 13

day13/part1.lua

@@ -0,0 +1,59 @@
+#!/usr/bin/env luajit
+require("utils")
+require("set")
+
+local file = io.open(arg[3])
+local coords = {}
+local maxr, maxc = 0, 0
+local line = file:read("*l")
+while line ~= "" do
+	local c, r = unpack(split(line, ","))
+	r, c = tonumber(r), tonumber(c)
+	if r > maxr then maxr = r end
+	if c > maxc then maxc = c end
+	table.insert(coords, { r, c })
+	line = file:read("*l")
+end
+
+local width, height = maxc + 1, maxr + 1
+foreach(coords, function(p) return p[1] * width + p[2] end)
+coords = set(coords)
+
+local folds = {}
+line = file:read("*l")
+while line ~= nil do
+	local dir, v = unpack(split(line, "="))
+	table.insert(folds, { dir == "fold along y", tonumber(v) })
+	line = file:read("*l")
+end
+
+
+for i, fold in pairs(folds) do
+	local dir, v = unpack(fold)
+	local ncoords = set()
+	for p in coords:iter() do
+		local r, c = math.floor(p / width), p % width
+		if dir and r > v then
+			r = 2 * v - r
+		elseif not dir and c > v then
+			c = 2 * v - c
+		end
+		ncoords:add(r * width + c)
+	end
+	coords = ncoords
+	break
+end
+
+for r = 0, height - 1 do
+	for c = 0, width - 1 do
+		if coords:has(r * width + c) then
+			io.write("#")
+		else
+			io.write(".")
+		end
+	end
+	io.write("\n")
+end
+io.write("\n")
+
+print(coords.size)

day13/part2.lua

@@ -0,0 +1,50 @@
+#!/usr/bin/env luajit
+require("utils")
+require("set")
+
+local file = io.open(arg[3])
+local coords = {}
+local line = file:read("*l")
+while line ~= "" do
+	local c, r = unpack(split(line, ","))
+	r, c = tonumber(r), tonumber(c)
+	table.insert(coords, { r, c })
+	line = file:read("*l")
+end
+
+local folds = {}
+line = file:read("*l")
+while line ~= nil do
+	local dir, v = unpack(split(line, "="))
+	v = tonumber(v)
+	if dir == "fold along y" then
+		for i, p in pairs(coords) do
+			if p[1] > v then p[1] = 2 * v - p[1] end
+		end
+	else
+		for i, p in pairs(coords) do
+			if p[2] > v then p[2] = 2 * v - p[2] end
+		end
+	end
+	line = file:read("*l")
+end
+
+local width, height = 0, 0
+for i, p in pairs(coords) do
+	if p[1] + 1 > height then height = p[1] + 1 end
+	if p[2] + 1 > width then width = p[2] + 1 end
+end
+foreach(coords, function(p) return p[1] * width + p[2] end)
+coords = set(coords)
+
+for r = 0, height - 1 do
+	for c = 0, width - 1 do
+		if coords:has(r * width + c) then
+			io.write("#")
+		else
+			io.write(".")
+		end
+	end
+	io.write("\n")
+end
+io.write("\n")