Fix O(n^2) network traversal

technic/machines/switching_station.lua

@@ -91,48 +91,57 @@ minetest.register_node("technic:switching_station",{
 --------------------------------------------------
 -- Functions to traverse the electrical network
 --------------------------------------------------
+local function flatten(map)
+	local list = {}
+	for key, value in pairs(map) do
+		list[#list + 1] = value
+	end
+	return list
+end
 
 -- Add a wire node to the LV/MV/HV network
-local add_new_cable_node = function(nodes, pos, network_id)
-	technic.cables[minetest.hash_node_position(pos)] = network_id
-	-- Ignore if the node has already been added
-	for i = 1, #nodes do
-		if pos.x == nodes[i].x and
-		   pos.y == nodes[i].y and
-		   pos.z == nodes[i].z then
+local function add_network_node(nodes, pos, network_id)
+	local node_id = minetest.hash_node_position(pos)
+	technic.cables[node_id] = network_id
+	if nodes[node_id] then
 		return false
 	end
-	end
-	table.insert(nodes, {x=pos.x, y=pos.y, z=pos.z, visited=1})
+	nodes[node_id] = pos
 	return true
 end
 
+local function add_cable_node(nodes, pos, network_id, queue)
+	if add_network_node(nodes, pos, network_id) then
+		queue[#queue + 1] = pos
+	end
+end
+
 -- Generic function to add found connected nodes to the right classification array
-local check_node_subp = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, pos, machines, tier, sw_pos, from_below, network_id)
+local check_node_subp = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, pos, machines, tier, sw_pos, from_below, network_id, queue)
 	technic.get_or_load_node(pos)
 	local meta = minetest.get_meta(pos)
 	local name = minetest.get_node(pos).name
 
 	if technic.is_tier_cable(name, tier) then
-		add_new_cable_node(all_nodes, pos,network_id)
+		add_cable_node(all_nodes, pos,network_id, queue)
 	elseif machines[name] then
 		--dprint(name.." is a "..machines[name])
 		meta:set_string(tier.."_network",minetest.pos_to_string(sw_pos))
 		if     machines[name] == technic.producer then
-			add_new_cable_node(PR_nodes, pos, network_id)
+			add_network_node(PR_nodes, pos, network_id)
 		elseif machines[name] == technic.receiver then
-			add_new_cable_node(RE_nodes, pos, network_id)
+			add_network_node(RE_nodes, pos, network_id)
 		elseif machines[name] == technic.producer_receiver then
-			add_new_cable_node(PR_nodes, pos, network_id)
-			add_new_cable_node(RE_nodes, pos, network_id)
+			add_network_node(PR_nodes, pos, network_id)
+			add_network_node(RE_nodes, pos, network_id)
 		elseif machines[name] == "SPECIAL" and
 				(pos.x ~= sw_pos.x or pos.y ~= sw_pos.y or pos.z ~= sw_pos.z) and
 				from_below then
 			-- Another switching station -> disable it
-			add_new_cable_node(SP_nodes, pos, network_id)
+			add_network_node(SP_nodes, pos, network_id)
 			meta:set_int("active", 0)
 		elseif machines[name] == technic.battery then
-			add_new_cable_node(BA_nodes, pos, network_id)
+			add_network_node(BA_nodes, pos, network_id)
 		end
 
 		meta:set_int(tier.."_EU_timeout", 2) -- Touch node
@@ -140,8 +149,7 @@ local check_node_subp = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nod
 end
 
 -- Traverse a network given a list of machines and a cable type name
-local traverse_network = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, i, machines, tier, sw_pos, network_id)
-	local pos = all_nodes[i]
+local traverse_network = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, pos, machines, tier, sw_pos, network_id, queue)
 	local positions = {
 		{x=pos.x+1, y=pos.y,   z=pos.z},
 		{x=pos.x-1, y=pos.y,   z=pos.z},
@@ -149,9 +157,8 @@ local traverse_network = function(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_no
 		{x=pos.x,   y=pos.y-1, z=pos.z},
 		{x=pos.x,   y=pos.y,   z=pos.z+1},
 		{x=pos.x,   y=pos.y,   z=pos.z-1}}
-	--print("ON")
 	for i, cur_pos in pairs(positions) do
-		check_node_subp(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, cur_pos, machines, tier, sw_pos, i == 3, network_id)
+		check_node_subp(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes, cur_pos, machines, tier, sw_pos, i == 3, network_id, queue)
 	end
 end
 
@@ -163,7 +170,8 @@ local touch_nodes = function(list, tier)
 end
 
 local get_network = function(sw_pos, pos1, tier)
-	local cached = technic.networks[minetest.hash_node_position(pos1)]
+	local network_id = minetest.hash_node_position(pos1)
+	local cached = technic.networks[network_id]
 	if cached and cached.tier == tier then
 		touch_nodes(cached.PR_nodes, tier)
 		touch_nodes(cached.BA_nodes, tier)
@@ -175,19 +183,28 @@ local get_network = function(sw_pos, pos1, tier)
 		end
 		return cached.PR_nodes, cached.BA_nodes, cached.RE_nodes
 	end
-	local i = 1
 	local PR_nodes = {}
 	local BA_nodes = {}
 	local RE_nodes = {}
 	local SP_nodes = {}
-	local all_nodes = {pos1}
-	repeat
+	local all_nodes = {}
+	local queue = {}
+	add_cable_node(all_nodes, pos1, network_id, queue)
+	while next(queue) do
+		local to_visit = {}
+		for _, pos in ipairs(queue) do
 			traverse_network(PR_nodes, RE_nodes, BA_nodes, SP_nodes, all_nodes,
-				i, technic.machines[tier], tier, sw_pos, minetest.hash_node_position(pos1))
-		i = i + 1
-	until all_nodes[i] == nil
-	technic.networks[minetest.hash_node_position(pos1)] = {tier = tier, PR_nodes = PR_nodes,
-			RE_nodes = RE_nodes, BA_nodes = BA_nodes, SP_nodes = SP_nodes, all_nodes = all_nodes}
+					pos, technic.machines[tier], tier, sw_pos, network_id, to_visit)
+		end
+		queue = to_visit
+	end
+	PR_nodes = flatten(PR_nodes)
+	BA_nodes = flatten(BA_nodes)
+	RE_nodes = flatten(RE_nodes)
+	SP_nodes = flatten(SP_nodes)
+	all_nodes = flatten(all_nodes)
+	technic.networks[network_id] = {tier = tier, all_nodes = all_nodes, SP_nodes = SP_nodes,
+			PR_nodes = PR_nodes, RE_nodes = RE_nodes, BA_nodes = BA_nodes}
 	return PR_nodes, BA_nodes, RE_nodes
 end