0041.bak

require 'primes'

def replace(buf, location, digit)
	count=0
	(0...buf.size).each do |i|
		if buf[i,1] == 'x'
			if count == location
				buf[i] = digit.to_s
				return
			end
			count+=1
		end
	end
end

largest = 0;

(0..7).each do |one|
	(0..6).each do |two|
		(0..5).each do |three|
			(0..4).each do |four|
				(0..3).each do |five|
					(0..2).each do |six|
						(0..1).each do |seven|
							num = "xxxxxxxxx"
							replace(num, one, 1)
							replace(num, two, 2)
							replace(num, three, 3)
							replace(num, four, 4)
							replace(num, five, 5)
							replace(num, six, 6)
							replace(num, seven, 7)
							replace(num, 0, 8)
							intval = num.to_i
							if intval > largest and intval.prime?
								largest = intval
							end
						end
					end
				end
			end
		end
	end
end

puts largest