solved part 1

day09/solution1.rb

@@ -0,0 +1,18 @@
+#!/bin/env ruby
+
+def valid_nums (nums)
+    nums.map { |num| nums
+        .map { |sub| sub + num if sub != num }}.flatten.uniq.compact
+end
+
+numbers = File.readlines('./input').to_ary.map(&:strip!).map(&:to_i)
+preamble = 25
+
+
+numbers.each.with_index do |number, i|
+    next if i < preamble
+    if !valid_nums(numbers[(i-preamble)..(i-1)]).include?(number)
+        puts number
+        break
+    end
+end