common/rle.lua


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-- run length encoding

local function encode(l)
	local out = {}

	local last = l[1]
	local count = 1

	local function ap()
		if count == 1 then
			table.insert(out,last)
		elseif count == 2 then
			table.insert(out,last)
			table.insert(out,last)
		else
			table.insert(out,{count,last})
		end
	end

	for ix=2,#l do
		local val = l[ix]
		if val == last then
			count = count + 1
		else
			ap()
			last = val
			count = 1
		end
	end

	ap()

	return out
end

local function decode(l)
	local out = {}
	for _,r in ipairs(l) do
		if type(r) == "table" and #r == 2 then
			for i = 1,r[1] do
				table.insert(out,r[2])
			end
		else
			table.insert(out,r)
		end
	end
	return out
end

return {encode=encode,decode=decode}