solved part 1

day02/solution.rb

@@ -0,0 +1,13 @@
+#!/bin/env ruby
+
+ids = File.readlines('./input').map(&:strip)
+checksum = {twos: 0, threes: 0}
+
+ids.map! { |id| id.each_char.tally.delete_if { |char, count| count==1 }}
+ids.each do |id|
+    checksum[:twos] += 1 if id.has_value?(2)
+    checksum[:threes] += 1 if id.has_value?(3)
+end
+
+puts checksum[:twos] * checksum[:threes]
+