AoC19/d03.lua

lines = {}
for text in io.lines(arg[1]) do
    line = {}
    for dir, dist in string.gmatch(text, "(%a)(%d+),") do
        table.insert(line, {dir=dir, dist=tonumber(dist)})
    end
    table.insert(lines, line)
end

function manhattan(x, y)
    return math.abs(x) + math.abs(y)
end
function sum(table)
    out = 0
    for _, x in ipairs(table) do
        out = out + x
    end
    return out
end

board = {}
intersect_p1 = nil
intersect_p2 = nil
function add_trace(x, y, index, steps)
    if not board[y] then
        board[y] = {}
    end
    if not board[y][x] then
        board[y][x] = {}
    end
    if not board[y][x][index] or steps < board[y][x][index] then
        board[y][x][index] = steps
    end
    if #board[y][x] > 1 then
        if not intersect_p1 or manhattan(x, y) < intersect_p1 then
            intersect_p1 = manhattan(x, y)
        end
        if not intersect_p2 or sum(board[y][x]) < intersect_p2 then
            intersect_p2 = sum(board[y][x])
        end
    end
end

min_x = 0
max_x = 0
min_y = 0
max_y = 0
for line_index, line in ipairs(lines) do
    pos_x = 0
    pos_y = 0
    steps = 0
    for trace_index, trace in ipairs(line) do
        if trace.dir == "U" then
            for y = pos_y + 1, pos_y + trace.dist do
                steps = steps + 1
                add_trace(pos_x, y, line_index, steps)
            end
            pos_y = pos_y + trace.dist
        elseif trace.dir == "D" then
            for y = pos_y - 1, pos_y - trace.dist, -1 do
                steps = steps + 1
                add_trace(pos_x, y, line_index, steps)
            end
            pos_y = pos_y - trace.dist
        elseif trace.dir == "L" then
            for x = pos_x - 1, pos_x - trace.dist, -1 do
                steps = steps + 1
                add_trace(x, pos_y, line_index, steps)
            end
            pos_x = pos_x - trace.dist
        elseif trace.dir == "R" then
            for x = pos_x + 1, pos_x + trace.dist do
                steps = steps + 1
                add_trace(x, pos_y, line_index, steps)
            end
            pos_x = pos_x + trace.dist
        end

        if pos_x > max_x then
            max_x = pos_x
        end
        if pos_x < min_x then
            min_x = pos_x
        end
        if pos_y > max_y then
            max_y = pos_y
        end
        if pos_x < min_y then
            min_y = pos_y
        end
    end
end

print("Part 1:", intersect_p1)
print("Part 2:", intersect_p2)

if arg[2] then
    out = io.open(arg[2], "w")
    out:write(string.format("P3\n%d %d\n255\n", max_x - min_x + 1, max_y - min_y + 1))
    for y = min_y, max_y do
        for x = min_x, max_x do
            if not board[y] then
                out:write("255 255 255 ")
            elseif not board[y][x] then
                out:write("255 255 255 ")
            else
                for i = 1, 3 do
                    if board[y][x][i] then
                        out:write("255 ")
                    else
                        out:write("0 ")
                    end
                end
            end
        end
        out:write("\n")
    end
    out:close()
end