Advent of Code 2016

advent_2016_1B.lua

local content = io.input("input.txt"):read("*a")
local coords = {0, 0}
local direction = {0, 1}

local visited = {}
visited[0] = {}
visited[0][0] = true

function check_overlap(old_coords, new_coords, direction)
	local x = old_coords[1]
	local y = old_coords[2]

	repeat
		x = x + direction[1]
		y = y + direction[2]

		if visited[x] == nil then
			visited[x] = {}
		end

		if visited[x][y] == nil then
			visited[x][y] = true
		else
			return math.abs(x) + math.abs(y)
		end

	until x == new_coords[1] and y == new_coords[2]

	return false
end

for turn, steps in content:gmatch("(%a)(%d+)") do
	steps = tonumber(steps)
	if turn == "L" then
		direction[1], direction[2] = -direction[2], direction[1]

	else
		direction[1], direction[2] = direction[2], -direction[1]
	end
	
	local new_coords = {
		coords[1] + direction[1] * steps,
		coords[2] + direction[2] * steps
	}

	local overlap = check_overlap(coords, new_coords, direction)
	if overlap then
		print("Found overlap at: ", overlap)
	end

	coords = new_coords
end

print("Finishing location: ", coords[1], coords[2])
print("Distance: ", math.abs(coords[1]) + math.abs(coords[2]))