Day 13, a very special spaceship.

1 files changed, 40 insertions, 0 deletions

diff --git a/day13/part2.rb b/day13/part2.rb
new file mode 100644
index 0000000..2a3bc0c
--- /dev/null
+++ b/day13/part2.rb
@@ -0,0 +1,40 @@
+def compare(left, right)
+  if left.is_a?(Numeric) && right.is_a?(Numeric)
+    left <=> right
+  elsif left.is_a?(Array) && right.is_a?(Array)
+    i = 0
+    t = nil
+    loop do
+      if left[i].nil? && right[i].nil?
+        t = 0
+        break
+      elsif left[i].nil?
+        t = -1
+        break
+      elsif right[i].nil?
+        t = 1
+        break
+      else
+        t = compare(left[i], right[i])
+        if t == 0
+          i += 1
+        else
+          break
+        end
+      end
+    end
+    return t
+  elsif left.is_a?(Array) && right.is_a?(Numeric)
+    return compare(left, [right])
+  elsif left.is_a?(Numeric) && right.is_a?(Array)
+    return compare([left], right)
+  end
+end
+
+packets = $stdin.readlines.map(&:strip).reject(&:empty?).map{ |l| eval(l) } + [[[2]], [[6]]]
+
+packets.sort! do |left, right|
+  compare(left, right)
+end
+
+puts (packets.index([[2]]) + 1) * (packets.index([[6]]) + 1)