Solution for Day 09

day_09/first.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+input = File.readlines('./input').map(&:to_i)
+preamble = 25
+
+input.each_with_index do |_line, i|
+  next if i < preamble
+
+  unless input[i - preamble, preamble].combination(2).find { |a, b| a + b == input[i] }
+    puts input[i]
+    return
+  end
+end