day 17

day17/part1.lua

@@ -0,0 +1,19 @@
+#!/usr/bin/env luajit
+require("utils")
+
+local xmin, xmax, ymin, ymax = string.match(io.open(arg[3]):read("*a"), "target area: x=(.*)%.%.(.*), y=(.*)%.%.(.*)")
+xmin, xmax, ymin, ymax = tonumber(xmin), tonumber(xmax), tonumber(ymin), tonumber(ymax)
+
+local maxdy = 0
+
+if ymax > 0 then
+	maxdy = ymax
+end
+
+if ymin < 0 then
+	if -ymin - 1 > maxdy then
+		maxdy = -ymin - 1
+	end
+end
+
+print(euler(maxdy))

day17/part2.lua

@@ -0,0 +1,34 @@
+#!/usr/bin/env luajit
+require("utils")
+
+local xmin, xmax, ymin, ymax = string.match(io.open(arg[3]):read("*a"), "target area: x=(.*)%.%.(.*), y=(.*)%.%.(.*)")
+xmin, xmax, ymin, ymax = tonumber(xmin), tonumber(xmax), tonumber(ymin), tonumber(ymax)
+
+local mindy = ymin
+
+local maxdy = 0
+if ymax > 0 then maxdy = ymax end
+if ymin < 0 then if -ymin - 1 > maxdy then maxdy = -ymin - 1 end end
+
+local mindx = 0
+while euler(mindx) < xmin do mindx = mindx + 1 end
+
+local maxdx = xmax
+
+local count = 0
+for odx = mindx, maxdx do
+	for ody = mindy, maxdy do
+		local x, y, dx, dy = 0, 0, odx, ody
+		while x <= xmax and y >= math.min(0, ymin) do
+			x, y = x + dx, y + dy
+			if xmin <= x and x <= xmax and ymin <= y and y <= ymax then
+				count = count + 1
+				break
+			end
+			if dx > 0 then dx = dx - 1 end
+			dy = dy - 1
+		end
+	end
+end
+
+print(count)

utils.lua

@@ -84,3 +84,6 @@ function bin2dec(str)
 	return v
 end
 
+function euler(n)
+	return n * (n + 1) / 2
+end