day 3 part 2

day3/part2.lua

@@ -0,0 +1,67 @@
+-- see if the file exists
+local function file_exists(file)
+	local f = io.open(file, "rb")
+	if f then
+		f:close()
+	end
+	return f ~= nil
+end
+
+-- get all lines from a file, returns an empty
+-- list/table if the file does not exist
+local function lines_from(file)
+	if not file_exists(file) then
+		return {}
+	end
+	local lines = {}
+	for line in io.lines(file) do
+		lines[#lines + 1] = line
+	end
+	return lines
+end
+
+-- tests the functions above
+local file = "input"
+local lines = lines_from(file)
+
+local input = ""
+for _, line in pairs(lines) do
+	input = input .. line
+end
+
+local instructions = {}
+-- print all line numbers and their contents
+for pos, a, b in string.gmatch(input, "()mul%((%d+),(%d+)%)") do
+	---@diagnostic disable-next-line: redefined-local
+	local a, b = tonumber(a), tonumber(b)
+	local product = a * b
+
+	instructions[#instructions + 1] = {
+		pos = pos,
+		product = product,
+	}
+end
+
+for pos in string.gmatch(input, "()do%(%)") do
+	instructions[#instructions + 1] = { pos = pos, enable = true }
+end
+
+for pos in string.gmatch(input, "()don't%(%)") do
+	instructions[#instructions + 1] = { pos = pos, enable = false }
+end
+
+table.sort(instructions, function(a, b)
+	return a.pos < b.pos
+end)
+
+local total = 0
+local enabled = true
+for _, instruction in ipairs(instructions) do
+	if instruction.enable ~= nil then
+		enabled = instruction.enable
+	elseif enabled then
+		total = total + instruction.product
+	end
+end
+
+io.output():write(total)