Add solution for 2015 day 12

2015/README.md

@@ -13,7 +13,7 @@
 | ✓      | 09  | Rust
 | ✓      | 10  | Ruby
 |        | 11  |
-|        | 12  |
+| ✓      | 12  | Ruby
 |        | 13  |
 |        | 14  |
 |        | 15  |

2015/day-12/.ruby-version

@@ -0,0 +1 @@
+3.0.0

2015/day-12/main.rb

@@ -0,0 +1,33 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "pathname"
+require "json"
+
+def sum_of_numbers(json)
+  case json
+  when Array then json.sum { |e| sum_of_numbers(e) }
+  when Hash then json.sum { |(_, v)| sum_of_numbers(v) }
+  when Numeric then json
+  else 0
+  end
+end
+
+def sum_of_numbers_nored(json)
+  case json
+  when Array then json.sum { |e| sum_of_numbers_nored(e) }
+  when Hash then json.value?("red") ? 0 : json.sum { |(_, v)| sum_of_numbers_nored(v) }
+  when Numeric then json
+  else 0
+  end
+end
+
+def main(file_paths)
+  file_paths.each do |file_path|
+    json = JSON.parse(file_path.read)
+    puts "#{file_path} / solution 1: #{sum_of_numbers(json)}"
+    puts "#{file_path} / solution 2: #{sum_of_numbers_nored(json)}"
+  end
+end
+
+main(ARGV.map { |x| Pathname(x) })