# frozen_string_literal: true input = File.readlines('./input').map(&:to_i).sort $d = { 1 => 0, 2 => 0, 3 => 0 } $j = 0 input << input.max + 3 input.each do |adapter| diff = adapter - $j if diff.between? 1, 3 $d[diff] += 1 $j = adapter end end puts $d[1] * $d[3]