[2022][ruby][9.2]

2022/ruby/day_09.rb

@@ -3,12 +3,12 @@ require "set"
 motions = ARGF.read.scan(/([RLUD])\s+(\d+)/).map { [_1, _2.to_i] }
 
 class Snake
-  attr_reader :tail
-
   def initialize
-    @head, @tail = [0, 0], [0, 0]
+    @knots = Array.new(10) { [0, 0] }
   end
 
+  def tail = @knots.last
+
   def move!(dir)
     delta = case dir
             when ?L then [ 0, -1]
@@ -17,14 +17,15 @@ class Snake
             when ?D then [-1,  0]
             else fail dir.inspect
             end
-    @head = @head.zip(delta).map { _1 + _2 }
+    @knots[0] = @knots[0].zip(delta).map { _1 + _2 }
+
+    (0...@knots.size-1).each do |i|
+      head = @knots[i]
+      tail = @knots[i+1]
 
-    delta = @head.zip(@tail).map { _1 - _2 }
+      delta = head.zip(tail).map { _1 - _2 }
       if delta.any? { _1.abs > 1 }
-      if delta.any?(&:zero?)
-        @tail = @tail.zip(delta.map { _1.clamp(-1, 1) }).map { _1 + _2 }
-      else
-        @tail = @tail.zip(delta.map { _1.clamp(-1, 1) }).map { _1 + _2 }
+        @knots[i+1] = tail.zip(delta.map { _1.clamp(-1, 1) }).map { _1 + _2 }
       end
     end
   end