Reforce 1, mario laps, exponentially slower to cover new ground

reforce1.lua

function tablelength(T)
  local count = 0
  for _ in pairs(T) do 
  	count = count + 1 
  end
  return count
end



emu.softreset();
emu.speedmode("maximum");

brain = {};

while (true) do
	emu.frameadvance();
	
	-- calculate frame hash
	checksum = 0;
	for x = 0, 255, 10 do
        for y = 0, 239, 10 do
        	r, g, b, palette = emu.getscreenpixel(x, y, false);
			checksum = checksum + palette
        end
    end
    if brain[checksum] == nil then
		brain[checksum] = {["start"] = 0, ["l"] = 0, ["lj"] = 0, ["j"] = 0, ["rj"] = 0, ["r"] = 0};
	end

	-- find least explored action for frame hash
	action = nil;
	tally = -1;
	for key in pairs(brain[checksum]) do
		val = brain[checksum][key]
		if action == nil or val < tally then
			action = key;
			tally = val;
		end
	end

	-- build input for frame hash
	jp = joypad.get(1);
	if action == "start" then
		jp["start"] = true;
		jp["left"]  = false;
		jp["right"] = false;
		jp["B"]     = false;
		jp["A"]     = false;
	elseif action == "l" then
		jp["start"] = false;
		jp["left"]  = true;
		jp["right"] = false;
		jp["B"]     = true;
		jp["A"]     = false;
	elseif action == "r" then
		jp["start"] = false;
		jp["left"]  = false;
		jp["right"] = true;
		jp["B"]     = true;
		jp["A"]     = false;
	elseif action == "lj" then
		jp["start"] = false;
		jp["left"]  = true;
		jp["right"] = false;
		jp["B"]     = true;
		jp["A"]     = true;
	elseif action == "rj" then
		jp["start"] = false;
		jp["left"]  = false;
		jp["right"] = true;
		jp["B"]     = true;
		jp["A"]     = true;
	elseif action == "j" then
		jp["start"] = false;
		jp["left"]  = false;
		jp["right"] = false;
		jp["B"]     = true;
		jp["A"]     = true;
	end
	joypad.set(1, jp);

	-- feedback brain
	brain[checksum][action] = brain[checksum][action] + 1

	fc = emu.framecount();
	if fc % 10000 == 0 then
		print(fc .. ": " .. tablelength(brain))
	end

	--gui.text(10, 10, tablelength(brain), "white", "black");
	--gui.text(10, 20, checksum .. ": " .. brain[checksum]["start"] .. ", " .. brain[checksum]["l"] .. ", " .. brain[checksum]["r"] .. ", " .. brain[checksum]["lj"] .. ", " .. brain[checksum]["rj"] .. ", " .. brain[checksum]["j"], "white", "black");

end