BFG10K program

program.lua

function middleofsquare(x)
	local m = tostring(math.pow(x, 2)):sub(4,9)
	m = m:match("^[0]*(%d*)") --trim leading zeros
	local offset = 1
	while(string.len(m) < 6) do
		m = tostring(math.pow(x, 2)):sub(4 - offset,9 - offset)
		m = m:match("^[0]*(%d*)") --trim leading zeros
		offset = offset + 1
	end
	return m
end

function findDup(...)
	local prev = 0
	local array = {...}
	table.sort(array)
	for _, num in ipairs(array) do
		if(num == prev) then
			return num
		end
		prev = num
	end
	return 0
end

function loop(seed)
	local results = {}
	table.insert(results, tostring(seed))
	while(true) do
		table.insert(results, middleofsquare(results[#results]))
		dup = findDup(unpack(results))
		if (dup ~= 0) then
			return seed, dup, #results
		end
	end
end

--~ Just some test cases to run
print("seed duplicate #results")
for v = 666666, 667000, 1 do
	print(loop(v))
end