Solution for Day 13

day_13/second.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+input = File.readlines('./input')
+
+$ids = input[1].split(',')
+$ids = $ids.map(&:to_i)
+
+$first = 0
+$period = 1
+
+$ids.each_with_index do |bus_period, id|
+  next if bus_period == 0
+
+  0.step do |i|
+    cand = $first + $period * i
+    if (cand + id) % bus_period == 0
+      $first = cand
+      $period = $period.lcm bus_period
+      break
+    end
+  end
+end
+
+puts $first