WIP Day 21

Author: ariejan

lib/input/day_21.txt

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+382A
+176A
+463A
+083A
+789A

lib/solutions/day_21.rb

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+require 'set'
+
+class Day21
+
+  def part_one(input)
+    sequences = input.split("\n")
+    sim = DayOne.new(sequences)
+    sim.run!
+  end
+
+  class DayOne
+
+    def initialize(sequences)
+      @sequences = sequences
+
+      @moves_cache = {}
+      @scores_cache = {}
+    end
+
+    # Define the numeric keypad with coordinates
+    NUMPAD = {
+      '7' => [0, 0],
+      '8' => [0, 1],
+      '9' => [0, 2],
+      '4' => [1, 0],
+      '5' => [1, 1],
+      '6' => [1, 2],
+      '1' => [2, 0],
+      '2' => [2, 1],
+      '3' => [2, 2],
+      ' ' => [3, 0],
+      '0' => [3, 1],
+      'A' => [3, 2]
+    }.freeze
+
+    # Define the directional keypad movements with corresponding commands
+    KEYPAD = {
+      ' ' => [0, 0],
+      '^' => [0, 1],
+      'A' => [0, 2],
+      '<' => [1, 0],
+      'v' => [1, 1],
+      '>' => [0, 2]
+    }.freeze
+
+
+    def xdir(x)
+      x > 0 ? 'v' : '^'
+    end
+
+    def ydir(y)
+      y > 0 ? '>' : '<'
+    end
+
+    def run!
+      result = 0
+      @sequences.each do |sequence|
+        value = Float::INFINITY
+        500.times do 
+          @moves_cache.clear
+          @scores_cache.clear
+          value = [value, score(sequence, 3, 0) * sequence[0..-2].to_i].min
+        end
+        result += value
+      end
+      result
+    end
+
+    def score(sequence, depth, current = 0)
+      cache_key = [sequence, depth, current]
+      # puts "scores_cache: #{@scores_cache}"
+      return @scores_cache[cache_key] if @scores_cache.key?(cache_key)
+
+      return sequence.length if depth == 0
+
+      total = current
+      sequence.chars.each_with_index do |key, index|
+        next_key = sequence[index - 1]
+        total += score(moves(next_key, key), depth - 1)
+      end
+
+      @scores_cache[cache_key] = total
+    end
+
+    def moves(current_key, next_key)
+      cache_key = [current_key, next_key]
+
+      return @moves_cache[cache_key] if @moves_cache.key?(cache_key)  
+  
+      # Pick the pad given the current and next key
+      pad = (KEYPAD.key?(current_key) && KEYPAD.key?(next_key)) ? KEYPAD : NUMPAD
+      
+      # puts "-" * 40
+      # puts "current_key: #{current_key}, next_key: #{next_key}"
+      # puts "#{KEYPAD.keys}"
+      # puts "pad: #{pad}"
+      # puts "pad[current_key]: #{pad[current_key]}, pad[next_key]: #{pad[next_key]}"
+      # puts "-" * 40
+
+      # Get x,y distances to move
+      distance = [pad[next_key][0] - pad[current_key][0], pad[next_key][1] - pad[current_key][1]]
+      # Map out key presses
+      presses = xdir(distance[0]) * distance[0].abs + ydir(distance[1]) * distance[1].abs
+
+      if pad[" "] == [pad[next_key][0], pad[current_key][1]]
+        result =  presses.reverse + 'A'
+      elsif pad[" "] == [pad[current_key][0], pad[next_key][1]]
+        result = presses + 'A'
+      else 
+        result = (rand < 0.5 ? presses : presses.reverse) + 'A'
+      end
+      
+      @moves_cache[cache_key] = result
+    end
+  end
+end

spec/input/day_21_test.txt

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+029A
+980A
+179A
+456A
+379A

spec/solutions/day_21_spec.rb

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+require "spec_helper"
+require "solutions/day_21"
+
+RSpec.describe Day21 do
+  let(:input) { File.read(File.join(__dir__, '..', '..', 'spec', 'input', 'day_21_test.txt')).strip }
+
+  describe '#part_one' do
+    it 'calculates the correct solutions for part one' do
+      expect(subject.part_one(input)).to eq(126384)
+    end
+  end
+
+  describe '#part_two' do
+    xit 'calculates the correct solutions for part two' do
+      expect(subject.part_two(input)).to eq(0)
+    end
+  end
+end
+