Naive but effective searcher for a short series of numbers comprised of alphanumeric characters that sum to a specific value, and intermediate values satisfy a bitwise constraint

lagos-search.rb

require 'Set'

def search_helper(nums, partial_sum, list, target, length, constraint)
	if list.length >= length - 1
		last = target - partial_sum
		if nums.include?(last)
			list << last
			return list
		end
	else
		nums.each do |num|
			n = (partial_sum + num) & 0xffff
			if n & constraint == 0
				res = search_helper(nums, n, list + [num], target, length, constraint) 
				return res unless res.nil?
			end
		end
	end
	return nil
end

# search for a series of alphanumeric numbers that add
# from start to target, where each intermediate sum & constraint == 0
def lagos_search(start, target, length = 3, constraint = 0)
	# build a list of all possible 16-bit alphanumeric numbers
	nums = Set.new
	bytes = ['0'..'9', 'A'..'Z', 'a'..'z'].map(&:to_a).flatten.map(&:ord)
	bytes.each_index do |i|
		bytes.each_index do |j|
			nums << (bytes[i] << 8 | bytes[j])
		end
	end

	return search_helper(nums, start, [], target, length, constraint)
end

if ARGV.length < 2
	puts "Usage: lagos-search starting_value target_value [length] [constraint]"
	exit(1)
end

res = lagos_search(Integer(ARGV[0]), Integer(ARGV[1]), Integer(ARGV[2] || 3) , Integer(ARGV[3] || 0))
if res
	puts res.map{|n| "%04x" % n}.join(',')
else
	puts "No solution found"
end