day 8, part 1

Author: Robb Kidd

2023/ruby/day08.rb

@@ -0,0 +1,63 @@
+require_relative 'day'
+
+class Day08 < Day # >
+
+  # @example
+  #   day.part1 #=> 2
+  def part1
+    parse(input)
+    steps = 0
+    node = "AAA"
+    @instructions
+      .cycle do |instruction|
+        break if node == "ZZZ"
+        steps += 1
+        node = @network[node][instruction]
+      end
+    steps
+  end
+
+  # @example
+  #   day.part2 #=> 'how are you'
+  def part2
+  end
+
+  # @example
+  #   inst, net = day.parse(EXAMPLE_INPUT)
+  #   inst #=> ["R", "L"]
+  def parse(input)
+    stanzas = input.split("\n\n")
+
+    @instructions = stanzas[0].chars
+
+    @network = {}
+    stanzas[1]
+      .each_line
+      .map { |line| line.scan(/\w+/) }
+      .each { |node, left, right|
+        @network[node] = { "L" => left, "R" => right }
+      }
+
+    [@instructions, @network]
+  end
+
+  EXAMPLE_INPUT = <<~INPUT
+    RL
+
+    AAA = (BBB, CCC)
+    BBB = (DDD, EEE)
+    CCC = (ZZZ, GGG)
+    DDD = (DDD, DDD)
+    EEE = (EEE, EEE)
+    GGG = (GGG, GGG)
+    ZZZ = (ZZZ, ZZZ)
+  INPUT
+
+  SIX_STEPS_INPUT = <<~INPUT
+    LLR
+
+    AAA = (BBB, BBB)
+    BBB = (AAA, ZZZ)
+    ZZZ = (ZZZ, ZZZ)
+  INPUT
+end