diff --git a/ruby/2019/4/bin/problem b/ruby/2019/4/bin/problem
new file mode 100644
index 0000000..8d93ed7
--- /dev/null
+++ b/ruby/2019/4/bin/problem
@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+
+require "secure_container"
+low, high = STDIN.read.chomp.split("-").map(&:to_i)
+range = low..high
+
+puts "Part 1: #{range.count(&:valid_part_1_password?)}"
+puts "Part 2: #{range.count(&:valid_part_2_password?)}"
\ No newline at end of file
diff --git a/ruby/2019/4/lib/secure_container.rb b/ruby/2019/4/lib/secure_container.rb
new file mode 100644
index 0000000..c82f420
--- /dev/null
+++ b/ruby/2019/4/lib/secure_container.rb
@@ -0,0 +1,25 @@
+class Integer
+  def valid_part_1_password?
+    has_two_adjacent_digits? and digits_never_decrease?
+  end
+
+  def valid_part_2_password?
+    has_exactly_two_adjacent_digits? and digits_never_decrease?
+  end
+
+  def digits_never_decrease?
+    digits.reverse == digits.sort
+  end
+
+  def has_two_adjacent_digits?
+    digits[..-2].zip(digits[1..]).any? { |x, y| x == y }
+  end
+
+  def has_exactly_two_adjacent_digits?
+    threes = digits[..-3].zip(digits[1..-2]).zip(digits[2..]).map{ |x| x.flatten(1) }
+    triple_indices = threes.each_with_index.select{ |trip, index| trip[0] == trip[1] && trip[0] == trip[2] }.map(&:last)
+    pairs = digits[..-2].zip(digits[1..])
+    pair_indices = pairs.each_with_index.select{ |pair, index| pair[0] == pair[1]}.map(&:last)
+    pair_indices.any? { |pair_index| !triple_indices.include?(pair_index) && !triple_indices.include?(pair_index - 1) }
+  end
+end