Ruby's standard library makes this so easy

ruby/2017/2/problem.rb

@@ -0,0 +1,55 @@
+class Row
+  attr_reader :values
+
+  def initialize(values)
+    @values = values.sort.reverse
+  end 
+
+  def self.for(string)
+    new string.split("\t").map(&:to_i) 
+  end
+
+  def to_s
+    values.to_s
+  end
+
+  def difference
+    values.first - values.last
+  end
+
+  def quotient
+    x, y = values.combination(2).find { |a, b| a % b == 0 }
+    x / y
+  end
+end
+
+class Spreadsheet
+  attr_reader :rows
+  def initialize(rows)
+    @rows = rows
+  end
+
+  def self.for(string)
+    new string.split("\n").map{ |row| Row.for row }
+  end
+
+  def to_s
+    rows.map(&:to_s).join("\n")
+  end
+
+  def checksum
+    rows.map(&:difference).sum
+  end
+
+  def evenly_divisible_values
+    rows.map(&:quotient).sum
+  end
+end
+
+sheet = Spreadsheet.for STDIN.read.chomp
+
+part_1 = sheet.checksum
+puts "Part 1: #{part_1}"
+
+part_2 = sheet.evenly_divisible_values
+puts "Part 2: #{part_2}"